ISO 10126 padding
A padding scheme that fills the gap with random bytes and records the padding length in the final byte.
ISO 10126 is one of the older standards for padding plaintext up to a block boundary. The filler is random, and the last byte gives the number of padding bytes. The idea was that randomness would make the padding less predictable than the zeros or repeated values used by ANSI X9.23 and PKCS#7.
In practice, the randomness added little and cost a lot of clarity. Few current libraries implement it, and you are unlikely to meet it outside old code and legacy protocols. If you do, treat it as a sign that the surrounding system has not been looked at in a while.