Guitar is the main playable instrument available in the Guitar Hero series. In all pre-Guitar Hero World Tour games lead guitar is the only playable guitar part. In Cooperative however lead could be played alongside of either bass or rhythm guitar.
Star Power is gained by hitting all star power notes in a star power sequence. Star power can also be gained by using the whammy bar on star power sustains. Star power can be activated by tilting the guitar up or by pressing the select button.
Chords are two or more notes played at the same time. For a chord to be played all corresponding fret buttons must be held. These can range from two to five notes played together. Chords occur more in hard and expert difficulties. As chords are two or more notes played together they are worth more than a single note. However, they're still counted as a single note on the note streak counter.
Sustains also known as long notes are a modified type of a regular note. Notes that have a tail on them are sustains. To play a sustain the correct note must be played and held down for the duration of the sustain. Releasing the fret button early won't penalize the player, but won't allow the player to receive additional points, and will mute the sound. Sustains can also be terminated by holding down a higher fret button or overstrumming. In all games prior to Guitar Hero III, using the whammy bar on a sustain provides additional points (and creates a warbling sound effect), however, from Guitar Hero III onward, the whammy bar's only particular benefit is extracting star power from sustains in a star sequence. Sustains can also appear in the form of chords.
Hammer-Ons and Pull-Offs (HOPOs) are types of notes used mainly for advanced players hence they are not as common as they are in hard and expert difficulties. The concept of HOPOs is to strum one note and play other notes by simply pressing the necessary buttons therefore hammering on or pulling off. HOPOs appear as regular notes except with light-colored tops. To start a HOPO sequence the first basic note before the HOPOs must be hit. The energy from this note will be passed on to the others. Hammer-ons will begin from a lower note to a higher note and pull-offs will begin on a higher note to a lower note. Pull-offs are the same, but in reverse.
Here's how they work: pressing a fret button is just like pressing all 6 strings on the neck of a guitar. As such, the fret button won't make a noise until the guitarist strums, causing the strings to vibrate. When multiple frets are pressed, the strings only vibrate at the fret closest to the body of the guitar, also known as, the highest note. As a result, the guitarist won't need to worry with the notes closer to the headstock of the guitar. Only the highest note will be played in these instances, a method called "High Note Override." For example, if a green sustain is played, and the red fret button is pressed, the sustain will be dropped. High Note Override does not apply when playing a chord. For example, if a red and yellow chord is about to be played, and the red and yellow fret buttons are pressed, but the green fret button is also pressed, the chord will not be played.
Guitar Hero: III and Guitar Hero: Aerosmith are the games in which a HOPO doesn't need to be hit when on the target so the necessary buttons can be held down just as basic notes can be.
In Guitar Hero: 5, Band Hero, and Guitar Hero: Warriors of Rock, chords began to be able to be part of HOPO sequences. These can also be harder to hit rapidly unlike with single note HOPOs.
Also introduced in GH: World Tour there is another type of note named the slider note. These are also known as tap notes. Slider notes appear as transparent gems with a rope connecting them. In GH: World Tour they have a purple rope which connects them and in later games a darker rope. Slider notes don't require strumming to be played. These can be played by using the fret buttons or using the slider.
Introduced in GH: World Tour a new type of note exists: extended notes. Extended notes are notes that extended past others. The notes which extended from the base note can be regular notes, chords, sustains, or slider notes. Sustains won't be dropped for holding the additional frets ahead of time or holding them after letting go of some of the frets. Though if a button is held that isn't in the extension then the note will be dropped.
The tutorial in Guitar Hero World Tour says that these notes only appear on Hard and Expert, however, this may have been an error on the developers' part, or it may have meant that these notes only appear to any significant degree on Hard and Expert, as these notes DO appear on Easy and Medium, albeit rarely. For example, "Pull Me Under" has an extended sustain on Easy for the bass, and "Hey Man, Nice Shot" has a few extended notes on Medium for the guitar(namely a green sustain that extends past multiple red notes.)
Alternate strumming is a technique which utilizes strumming both up and down. This makes faster strings of notes more easy to hit.
Tapping is an advanced used to play difficult sections more easily. Tapping makes use of the High Note Override method where while holding multiple buttons only the highest note counts unless playing a chord. Tapping is used on sections comprised mostly of HOPOs or Slider Notes. Tapping is used by the anchoring (holding) the lower note down and pressing the higher fret button(s). Tapping can be done with one or both hands. Tapping with both hands should be used only where there are more notes per second.
Squeezing is another advanced technique. Squeezing is used to 'squeeze' additional points in a Star Power use. This technique takes advantage of the size of the timing window. Squeezing is done by playing a note late and using Star Power before the note is played and playing a note at the end of the use early. In doing this two additional notes are gained in the Star Power use: one in the beginning and on in the end. Squeezing is difficult to master due to the fraction of time to be used in it.
Elbow strumming, as the name implies, is the strumming of a note with the elbow. Elbow strumming is used when the player is about to use tapping and already has both hands on the fret buttons.
Overstrumming is the occurrence of strumming more than what is needed. Overstrumming can occur most often in extended strings of notes.