Barber well said, could not have delineated any better, a great example is for instance the New England Family. Right now presently, we have the Boss Peter Limone on 5 year probation from any felon and crime family members and associates, which has severed him from guiding and conducting any kind of business. So the Street Boss is believed to be Anthony Dinunzio, who is recognized as the Boss on the street calling the shots, but the title is held by Limone.

Liborio Bellomo is running the day to day operations of the Genovese crime family as a sort of unofficial boss while danny leo is in prison assuming Leo holds the title of acting boss/boss still

I think in the generic sense a Street Boss is the head captain of a family that has a bit of influence with the other captains and also with his superiors. He looked at as a more approachable and down to earth boss than the official one.

I don't really see it as being the same as the acting boss, who is official a steward in the role for the official boss. I think for the most part these colloquial street bosses have their own crew. To put it into a fictional perspective, think about Tony Soprano early on in the show. Junior was boss and had his administration. Yet Tony was viewed as being ina position of authority on par if not higher than Junior with the guys on the street.

Also, on another note apparently the Colombo family had created a new position of Street Boss (directly answerable to the official boss) as a way to insulate himself. And to have more hands on crontrol of the crews by proxy.