That has to do with the guages of the strings, of which there are a myriad of combinations. The guages of the strings also affect the action and relief of the neck and fretboard. I'll give you my favorites, if you don't know. There are many more combinations of guages, but these are common:
For electrics, I like "tens", or "lights":
.010, .013, .017, .027, .039, .046
If you prefer lighter guages, "nines", or "extra lights":
.009, .011, .016, .025, .033, .043
For acoustics, I like "twelves", or "lights":
.012, .016, .025, .032, .042, .052
If you prefer heavier guages, "thirteens", or "mediums":
.013, .017, .026, .035, .045, .056
When they ask for your Band Name - Ukulele Underground
Your Band Website -
http://www.ukuleleunderground.com/forum
Maybe they'll direct freebies and promotions over here! Ric