Mode 2 Form 1 (M2F1)

Mode 2 Form 1 is a data mode designed to fit in the Mode2 tracks.
A Track in a certain mode (Audio, M1, M2) HAS to contain block in that same mode.
By changing the form, M2 tracks can contain sectors with Mode 2, Mode 2 Form 1 and Mode 2 Form 2. 

If extracted raw you end up with 2352 bytes per block.
2048 (2K) bytes are user data (the data you actually find in the files)
The remainder of the data contains : sync bytes, header bytes, subheader bytes and third layer error correction bytes (EDC and ECC)

This mode is the most popular Data block mode used by write applications.  Stamped data CDs are largely still Mode 1.