Education

The term "dropout" means a child who quits school before graduation. Compare pushout, a child counseled or forced out of school before graduation.

Telecommunication

The term dropout has the following meanings:

1. In a communications system, a momentary loss of signal.

Note: Dropouts are usually caused by noise, propagation anomalies, or system malfunctions.

2. A failure to read properly a binary character from data storage.

Note: A dropout is usually caused by a defect in the storage medium or by a malfunction of the read mechanism.

3. In magnetic tape, disk, card, or drum systems, a recorded signal with an amplitude less than a predetermined percentage of a reference signal.

Source: from Federal Standard 1037C and from MIL-STD-188

Cycling

Slots in a bicycle frame where the axle(wheel) is attached.
Horizontal dropouts allow adjustment of chain tension, and can accommodate a range of chain lengths or cog sizes. They are typically used by single-speeds.
Vertical dropouts necessitate another means of chain-tensioning, by a derailleur or chain tensioner

Astronomy

A dropout is a source whose radiation disappears shortward of a given filter. Looking for dropouts is an usual method to look for high redshift galaxies.