The only three words you need to know in a military barber shop. A high and tight haircut is one in which the back and sides of the head are shaved down to a fine stubble and the top is left "long," by which I mean about a half-inch long. Depending on the shape of your head, the barber, your unit, how high speed you are, and the branch of the armed forces you're in, this can vary wildly. A high and tight saves shampoo and bathroom time in the morning, but requires maintenance about once every two weeks to stay sharp-looking. If left alone, a high and tight can be in regs for over a month.
Because the standards and regulations for an "acceptable" haircut are so lax in today's armed forces, you won't see everyone with a high and tight, but most Marines will be whitewalled, as will most of the hardcore combat arms troops you meet. A high and tight haircut is one way a person in the military can show pride in their job. Just because it's the minimum doesn't mean it's good enough.
Like a spit shine and a perfectly starched uniform, it's one more aspect of the military appearance that says "I'm so good at fighting, I can spend the rest of my free time just trying to look hardcore." | 
