an intervening period of time

an interval of 50 years.

a period of temporary cessation; pause

intervals between the volleys of gunfire.

a space between things, points, limits, etc.; interspace

an interval of ten feet between posts.

Mathematics .

the totality of points on a line between two designated points or endpoints that may or may not be included.

any generalization of this to higher dimensions, as a rectangle with sides parallel to the coordinate axes.

the space between soldiers or units in military formation.

Music . the difference in pitch between two tones, as between two tones sounded simultaneously (harmonic interval) or between two tones sounded successively (melodic interval).

Chiefly New England . intervale.

Cards . a period in a game for placing bets.

British . an intermission, as between the acts of a play. ?

at intervals

at particular periods of time; now and then

At intervals, there were formal receptions at the governor's mansion.

at particular places, with gaps in between

detour signs at intervals along the highway.