Tools

Saws

A miter is and angled joint[1].

A miter saw (or mitre saw) helps such joints -- and anything else that is served by well controlled angles

Classically this was mechanical:

assists such angled cuts using a regular handsaw in

the simplest variant is just wood with slits that guide 45 (and 90) degree angles

miter saw - the most basic thing you could call 'miter saw' is a handsaw guided by a mechanical mount - like a miter box with non-detachable saw

(and replacable blade)

preferable in that miter boxes tend to degrade with use, so this is more reusable and often more precise

Power miter saws are the variants that are motorized, mainly:

brings down a saw head, at a controlled angle.

(a chop saw is this without the angle control, always cutting right, 90 degree angles)

adds tilt of the head

(sometimes the basic rotation may be a little more aribitrary/controlled than in a basic variant)

Options / details:

sawblade extends on a sliding rail, rather than only being brought down

can deal with somewhat larger boards

ability to angle to both sides rather than one (and, less commonly, to tilt to both sides)

easier to do certain cuts readjusting the saw rather repositioning than the workpiece

a little more precision

Because this is a collection of features realized in different combinations

some may be unique to areas (or industries)

and may have specific names in some areas of the world that they do not have in others.

Sort of like a table saw without a table.

Generally for wood, though variations for e.g. metal and concrete may vary in design, not just mounting a different blade.