Hacker... space. It's a "space"... where people "hack" on their projects. Seems pretty straightforward. The only part that throws people off is the definition of the term "hack," though these days surely we're beyond thinking that's just people who break into computers?

Hackerspaces generally have machine shops, but that's not all they are. They also have lounges, computer labs, biotech labs, kitchens, and whatever else their respective members are interested in.

Definitely not! The place is open to visitors most every evening. Any of the events on the calendar are open-house events: http://atxhackerspace.org/wiki/Calendar

No, there is definitely welding, as well as dozens of other things that were not mentioned in the video.