a tempo

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adverb & adjective In the tempo originally designated; resuming the initial tempo of a section or movement after a specified deviation from it. Used chiefly as a direction.

from The Century Dictionary.

• noun In music, a direction, after any change of movement, as by acceleration or retardation, that the original time be restored.
• Various qualifying terms are often added: as, a tempo commotio or ordinario, at any conveuient or ordinary pace: a tempo rubato (see rubato).