1. A waveguide phenomena; see channel wave. 2. A configuration of rocks which is able to confine fluids (such as oil) which float on other fluids (water). A closed structure in porous formations may be a trap if it has an impermeable cap; an unclosed structure may also be a trap if permeability variations block the escape route of fluids. Compare closure. 3. A CPU-initiated interrupt which is generated when a predetermined condition, such as an illegal instruction, breakpoint, specified error, or power failure, is detected.