The phrase "grabs some z's" is a colloquial expression for sleeping or taking a nap. There are numerous synonyms for this phrase, including catching some shut-eye, sleeping like a log, grabbing forty winks, getting some rest, hitting the hay, dozing off, taking a siesta, and snoozing. Each of these expressions refers to taking a short nap or getting some sleep, whether it's during the day or at night. Depending on the context, some of these expressions may be more appropriate than others when referring to the act of taking a nap. Ultimately, however, they all refer to getting some much-needed rest.