What does C2B. C2F.means in knitting?

C2B = Cable 2 back. C2F = Cable 2 front.

Usually you will find the definitions for knitting abbreviations in the header section of your pattern. Although these two abbreviations are fairly common they are often used for different types of cable depending on the design of the garment.

C2B could mean "slip the next two stitches onto a cable needle and hold at the back, knit the next two stitches on the left hand needle and then knit the two stitches on the cable needle."

Or it could mean "slip the next two stitches onto a cable needle and hold at the back, knit the next stitch on the left hand needle and then knit the two stitches on the cable needle."

Or it could mean "slip the next stitch onto a cable needle and hold at the back, knit the next stitch on the left hand needle and then knit the stitch on the cable needle."

Your best bet is to check the pattern to find the definition used by the designer.

Please note: The general accepted abbreviation C2B (Cross 2 Back) and C2F (Cross 2 Front) are generally formed using method 2 above (i.e., "slip the next two stitches onto a cable needle and hold at the back, knit the next stitch on the left hand needle and then knit the two stitches on the cable needle.").