Common abbreviations include:
.00 CYL - cylinder
.05 SKEET - skeet
.10 IC - improved cylinder
.15 LM - light modified
.20 MOD/M - modified
.25 IM/IMOD - improved modified
.30 LF/LIGHT Full - light full
.35 FULL - full
.40 Xtra Full
The first number is are the points of constriction (POC), a measurement of how much tighter the choke is than the bore diameter. These are general figures. If you actually take a micrometer to individual choke tubes, you'll find that there is some variance. Also, some manufacturers may use slightly different designations. For example, you may see something like SKEET2, which IIRC is around LM in terms of constriction.