TAK/OEE is an abbreviation for "Overall Equipment Efficiency", and it's a way of measuring production efficiency. Below is a short introduction to how OEE is calculated. OEE consists of three parts, A = Availability, P = Performance, and Q = Quality.

These parameters all affect the final OEE number in their own way, as shown below.

[A]vailability: This is measured as part of the planned production time that the machine was running. The remaining time is various types of stops, either scheduled or not scheduled. The result is shown in % - percentage -. 

[P] erformance: This takes into account slow cycles, stops, unforeseen breaks, etc.

[Q]uality: The quality yielded over time, it is measured as the percentage of good quantity in relation to the number of produced quantity.

Calculation of the parts contained in the OEE number

[A]vailaility = (run time - stop time) / scheduled time.
Availability is a number that describes how much of the maximum possible production time the machine actually produced. At a facility where there are two shifts a day, each consisting of 8 hours, 16 hours would be the maximum theoretical number of production hours.

[P]erformance = measured production / ((scheduled time - stop time) * optimal production).
This number tells us how fast, compared to the theoretical maximum, production is going when the machine is running.

[Q]uality = (produced quantity - scrap) / produced quantity.

Quality is the result of the percentage of produced units, that are approved, minus any/all failed production units that did not meet the quality standards. 

When all of the above numbers are calculated, they are multiplied by one another, which results in the OEE number. A * P * Q = OEE.
When studying the above numbers, one can conclude that all factors must be high to yield a good OEE number.