What's the proper term for "brain waves" read from an EEG?
The terminology around EEGs is variable, dependent on the context; 


Brain wave is fine, but has a bit of a popular undertone;
Oscillation, as per the deleted answer,  implicitly refers to a longer-term behavior, i.e., something periodic (EEG);
Waveform is often used to describe a single event with a recognizable shape (ERP, compound action potentials, etc.);
EEG signal/recording/trace is more than fine too, it doesn't carry any implicit meaning about its nature, it does carry relevant information on the method used;
EEG is fine too, EEG means electroencephalogram, the 'gram' suffix comes from Greek, where it means “something written,” or a “drawing”, so literally it means something like "graph of the electrical brain". So simply speaking of 'the EEG' is OK as well.


This list may not be exhaustive, merely illustrative