Actually, a more appropriate explanation for the quote made by Corporal Ferro
can be found by thinking about her previous line.
'.. in the pipe, five by five..'
As they were coming down through some pretty rough atmospheric conditions, you'd think they'd be on an Instrument Landing System (ILS) of some kind. These commonly display the 'pipe' down which a pilot must fly as a series of squares, the middle of which the pilot must fly down.
Number the squares edges from 1 to 10, horizontally and vertically, and the quote 'five by five' makes a lot more sense. I have no idea if this is a more 'normal' usage than the radio signal / clarity use described above. However, the idea that the colonial marines considered themselves in deep shit when they went down onto the planet is incorrect - the attitude of the marines was derisory towards Ripley, and her description of the Aliens. They are the best of the best, and have no fear of what they're going into.
I am ready, man. Ready to get it on. Check-it-out. I am the ultimate badass... state of the badass art. You do not want to fuck with me. Hey, Ripley, don't worry. Me and my squad of ultimate badasses will protect you. Check-it-out...
Independently targeting particle-beam phalanx. VWAP! Fry half a city with this puppy. We got tactical smart-missiles, phased-plasma pulse-rifles, RPG's. We got sonic electronic ballbreakers, we got nukes, we got knives... sharp sticks
The colonial marines have no idea what they are going into, and one of the finer points of the movie for me is how quickly these weapons become mere toys against the alien menace. Superb movie.