Below we offer diagrams of both acoustic and electric instruments and their most commonly mentioned parts. Some items are, of course, common to both types of instruments (headstock, tuners, fretboard, strings, etc.) Cases such as those are not repeated.
Strings: although traditional guitars employs six strings, there are guitar variations that can use up to fourteen strings,
Neck: roughly, the piece of wood that extends from the body of the instrument, where the fretboard, frets, and headstock are placed.
Headstock: it is the part of the instrument that holds the strings and, usually, those are fixed to the headstock by means of tuning pegs. Each major guitar brand has a number of signature headstocks that make their instruments easily recognizable.
Tuners: also called machine heads or tuning pegs, they are used to tune the instrument by changing the tension of the strings. They are also found in mandolins, banjos, double basses, etc (as opposed to violins, violas, etc. which employ friction pegs). The pinion and worm gear mechanism is traditionally exposed in classical guitars, whereas acoustic and electric guitars usually have them enclosed. Tuning pegs can be arranged in a number of ways, depending on the shape of the headstock: the most common arrangements are three pegs to each side, or all six in a diagonal line (as in Stratocaster electric guitars).
Fretboard: also called fingerboard, it consists of a long strip of wood laminated to the neck of the guitar. The strings run over it, and they are pressed against it to create different pitches. Though in the guitar the fingerboard is usually fretted, other instruments employ unfretted fingerboards or a combination of the two.
Frets: metal strips inserted into the fingerboard that divide it into semitones, defining the spaces where the strings should be stopped.
EQ: electro acoustic guitars (those with fitted electronics for amplification) will usually have a set of plastic controllers, providing simple EQ options for the microphone, as well as overall gain. Some manufacturers insert special features on this controllers, such as in built tuners.
Body: the body plays a major role in defining the sound of acoustic instruments. String vibration is transmitted though the bridge and saddle to the soundboard, and the shape of the cavity and soundhole have an impact on the final sonority.
Sound Hole: though technically most of the sound of the guitar comes from the body itself (the sounding board, to be precise), the sound hole allows the instrument to project sound in a more efficient way. They come in a variety of shapes and sizes, though the most usual design is circular, surrounded by a rosette pattern.
Scratch Plate: also called pickguard, it is a piece of laminated material (often plastic) used to prevent the plectrum from scratching the body of the guitar.
String Pins: also called bridge pins, they lock the strings to the guitar, also playing an important role in transferring vibrations to the body. They are made of bone or synthetic elements.
String Tree: employed in some electric popular guitar models (such as the Stratocaster) to hold the strings in place.
Truss Rod Access: through this opening (encased in some models) a luthier may access the truss rod, a long steel rod that runs inside the neck of the guitar, which can be adjusted to adjust its curvature.
Nut: a piece of bone, plastic, brass, or any synthesized material of similar consistency, that is placed at the top of the fretboard to guide the strings into it in a parallell fashion and keeping the appropriate distance from each other.
Inlay markers: used as a form of reference to quickly locate certain frets, they are popular in electric and acoustic guitar, but rarely seen in classical guitar. Some companies design their signature inlays (such as PRS's signature birds inlay). Sometimes, there will also be tiny markers on the edge of the neck that faces the guitarist.
Strap pin: used to fit the guitar strap, they come in a variety of shapes and mechanisms.
Pickups: electronic pieces that detect string vibration and transform it into electrical energy for amplification. Traditionally, they come in single and double-coil varieties, the later being less prone to pick up interference. They can either require batteries or be passive. The type and make of pickups play a big part in the final sound of the instrument.
Selector switch: used to control which pickups are active, they are an essential tone shaping tool for the electric guitarist. They can have two, three, five, or more positions, depending on the type of pickups, the electronic, and the combination possibilities.
Tone/Volume controls: they control the amount of output gain and the bass/treble balance. Depending on the type of guitar, there may be one or two tone controls and one or two volume controls.
Output jack: where the cable is plugged in to amplify the guitar.
Brige: used to transfer the vibration from the strings to the body, it also holds the strings in place. Bridges come in a wide variety of designs, some including mechanisms for fine intonation. Some bridges come with an opening for a whammy bar or (wrongly called) tremolo arm to be inserted. These models are spring-loaded and capable of subtly moving to let the guitarist change the tension of the strings (and therefore change the sounding pitch) using the whammy bar. Modern electric instruments come with a saddle system on the bridge that allows for fine calibration.