What is a regular hacksaw?

Most probably this refers to a hand hacksaw, which uses blades of about 10 inches or so. The blades are made with various different number of teeth per inch.

Commonly, from about 18 t.p.i, to 24 t.p.i, which would be used for cutting thin tube or sheet metal. There are also some small hand hacksaws with blades of only about 6 inches, for light work, or confined spaces.

Blades are also made with 'variable pitch' running from 24 t.p.i. at one end of the blade, to about 18 t.p.i. at the other. These are very useful, as it is easier to get started with the fine pitch, then to move on to the coarser pitch at full stroke, once the cut has been established.

Metal cutting saws are also made as band saws, and as reciprocating saws.