Sentence:  These reliably variable objects included three ROCOSs (OE 400, OI 090.4, and PI034-293) and two <WSD>lacertids</WSD> (AO 0235+164 and OJ 287). 
Meaning of the word marked with <WSD> tags:  A type of blazar (highly variable active galactic nucleus) that lacks spectral emission lines characteristic of quasars.