1. To cause a reduction in the atmospheric pressure of an enclosed space, or to experience such a reduction: The newly invented mini-machine was used to decompress the vacuum tube in the laboratory.
2. To allow a substance to expand to normal dimensions or volume by the removal of pressure, or to undergo this process: When the diver rose to the surface of the sea, he slowly decompressed himself so as not to become ill.
3. To relax or to unwind; especially, after being busy or stressed: After work, Shirley found that a good cup of tea helped her to decompress and to feel at ease.
4. To expand compressed electronic, or computer, data to its normal extent, or to undergo this process: The instructor said that if anyone hits a certain button, he or she will decompress the files in the computer and be able to read them.