MIDI devices are primarily used by musicians to make music, time is basically expressed in terms of Beat Per Minute (BPM). The speed of the beats are called Tempo. A tempo of 60 bpm signifies that there are 60 beats per minute. That is because of there are the same number of seconds, which means one beat per second. You may calculate other time relationships, such as 120 bpm which is 2 beats per second, or 1 beat per half second. There is the concept of doubling and dividing/halfing the numbers.
Meters also group beats into units called "Measures", and the number of "Beats per Measure"(NOT BPM). The measures are in meters which represents in music by a Meter Signature or Time Signature. These are written in a fraction format. Here is an example, 4/4 which is a meter of 4 beats per measure. The top number represent the beats and bottom represents the measures. 4/4 Meter means there are 4 beats in a measure, and 1/4 quarter note gets one beat. This means if the Tempo is 120 BPM, each quarter note which is a beat is a half-second long, there will be two per second, and a measure of 4 quarters will last 2 seconds.
There is a relationship between beat, bpm, and minutes, so with a little math, any tempo can be calculated. In beats though, using fractions smaller than 16th notes gets a little cumbersome, musicians do not use them that much at all. So instead, most devices use something called"tick" or clock value. Ticks are measured in parts per quarter notes (ppqn). For example, a ppqn of 480 means there are 480 units parts per quarter note and 120 per 16th note. Notice that 480 can be divided by 60. This means more whole numbers will flow, and it will be able to come out in seconds, when an even will happen in musical time.
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