At attention

The position of at attention, or standing at attention, is a military posture which involves the following general postures:

The above stance position is common in most military organizations throughout the world. It may also be adopted by paramilitary organizations, law enforcement, and other organizations requiring a loosely military structure such as Scouts, cadet programs, or police units, or even the Salvation Army.

It is also used in common in civilian marching bands, fife and drum corps and drum and bugle corps. To stand at attention is also a means of saluting when a junior rank meets an officer or superior but he (the junior) is not wearing a hat.

...
Wikipedia