The Gemara (6a) tells us about "Mevo'ot she'Einan Mefulashim," "alleys which are not open from one end to the other." In the times of the Talmud a few houses opened into one Chatzer, courtyard, and a few courtyards opened into a Mavuy, or alley, so an "alley" refers to a busier street.

Just a few lines earlier, the Gemara mentions "Mevo'ot ha'Mefulashim," alleys which are open from one end to the other. This is similar to a busy street which is open at both ends, while the "Mevo'ot she'Einan Mefulashim" are streets which finish in a dead end.

All the best,

Dovid Bloom