The term perfect identifies this interval as belonging to the group of perfect intervals, so called because of their extremely simple pitch relationships resulting in a high degree of consonance. "Perfect" distinguishes the perfect fourth from the augmented fourth, which is one chromatic semitone larger.
A helpful way to recognize a perfect fourth is to hum the starting of the "Bridal Chorus" from Wagner's Lohengrin ("Treulich gefuehrt," the colloquially titled Here Comes the Bride), which is a familiar perfect fourth.
The perfect fourth is a perfect interval like the unison, octave, and perfect fifth, and it is a sensory consonance. In common practice harmony, however, it is considered a stylistic dissonance in certain contexts, namely in two-voice textures and whenever it appears above the bass. If the bass note also happens to be the chord's root, the interval's upper note almost always temporarily displaces the third of any chord, and is then called a suspended fourth.
Conventionally, the strings of a double bass and a bass guitar are tuned by intervals of perfect fourths, as well as all but one of the strings of a guitar. It is also a very common musical interval to which tom-tom drums are tuned.