1. To cover with lagging to prevent heat loss
2. To hang (back) or fall (behind) in movement, progress,

Last, hindmost

A brief delay.
A saturation effect whereby the signal from an instrument endures beyond the response time after the target has been removed from the field of view. Can be caused by exposing the sensor to a target of high temperature for an extended period. The effect is expressed as the increase in response time required for the sensor to return to within 5% of the correct reading.
A time delay between the output of a signal and the response of the instrument to which the signal is sent. 2. A time relationship between two waveforms where a fixed reference point on one wave occurs after the same point of the reference wave.

The time difference between two events. In electronics, a lag is a delay between a change in input and a change in output. On computer displays, a lag is a fading brightness left on the phosphor coating of the screen after an image changes. See also persistence.