Yep, that's a "freeze plug", although it isn't there to protect the block from cracking when the coolant freezes, like some people believe. The holes are there so the foundry can knock the sand out of the cooling passages after the block is cast. Then the openings are machined true and steel plugs are driven in when the engine is built up at the factory. After some time, they rust out and leak. Drive a hole in the bad plug with a sharp punch and pry it out, then drive a new one into place with a little Permatex on the edge as a sealer. There are rubber expansion-type plugs available to replace freeze plugs in tight places if it's not convenient to put a drive-in plug back into place. Wnen I do an out-of-frame rebuild, I replace all the freeze plugs with brass ones that resist rusting.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!