Frame rate is to frequency as ____ is to period?
If a video has a frame rate of 25 fps, the video has a 40ms ____?
frame duration: The time between the beginning of a frame and the end of that frame. Note: For fixed-length frames, at a fixed data rate, frame duration is constant.
The normal use (at least in my experience, I have a technical/scientific background) is to say the interval as the elapsed time between events that happen with a known frequency. So if interval is the reciprocal of rate then we might think that frame interval is the reciprocal of frame rate.
However in regards to video, this does not appear to be in common usage. Typical video encoding techniques do not encode complete frames of video, only partial frames are encoded (to reduce the size of the video data). The distance betyween the full frames is normally known as an interval - either the Key Frame interval of the I Frame interval depending on the encoding sceheme, software tools and audience.
Mention of "Frame Interval Timing" which is relevant to a particular manufacturer of cameras.