OSC specifies the syntax of messages and their data at the level of bits and bytes. Knowing that a given sequence of bytes is an OSC Packet allows you to parse those bytes into groups of messages (containing human-readable address patterns plus type-tagged binary data) that may have timestamps. hat the messages "mean" or what the receiver "should do with them" is fully opt-in.
OSC is a content format.
OSC plus agreed semantics (for a given use case) would together comprise a protocol.