This article is from the Secure Sockets Layer Discussion List FAQ, by Shannon Appel SAppel@consensus.com with numerous contributions by others.
... It appears that information can be sent only in blocks. Does
there have to be a one-to-one mapping between write() calls on the
client/server and SSL records? Is there some other blocking
taking place when user data is being sent?
The record layer takes a data stream from the higher layers and
fragments it into records. If the write is longer than 2^14 bytes
(with headers), the record layer will generate multiple records.
Multiple writes can be condensed into a single record.