What does "Pit-bull terrier" mean in the etymology explanation of pit?

"hole," O.E. pytt "water hole, pit," from W.Gmc. *puttjaz "pool, puddle" (cf. O.E. putti, O.N. pyttr, Du. put, Ger. Pfütze), early borrowing from L. puteus "well, pit, shaft." Meaning "abode of evil spirits, hell" is attested from early 13c. As a verb, “to put into a pit,” mid-15c.; especially for purposes of fighting (of cocks, dogs, pugilists) from 1760. Figurative sense of “to set in rivalry” is from 1754. Meaning “to make pits in” is from late 15c. Related: Pitted; pitting. Cf. Pit-bull terrier first recorded 1945. This is also the notion behind the meaning "the part of a theater on the floor of the house" (1640s). Pit of the stomach (1650s) is from the slight depression there between the ribs.