In TCP, something called the 'push flag' can be set to cause accumulated data in the monitor (which may be one or more packets) to be sent over the network.  It is often abbreviated as "PSH".

The Tops-20 FTP client and server both set PSH on the last packet of data from a file to send it on its way.  This is done with a SOUTR% JSYS, which stands for String OUT Record.  This is an overloading of the hardware record concept which is more commonly associated with nine-track magnetic tape.

PSH can also be detected on input by doing a SINR%, which stops the network read early, instead of waiting for a full buffer of data (which might, in fact, never come).

I believe DECnet transport implements the same semantics, but I would like to double check that.  Where would I go in which part of what specification?  Or does anybody know?