If someone is described as searching “high and low,” it means that he or she is looking for something or someone in every imaginable location. Such a search would encompass practically every place that a person could think of looking, and it likely wouldn’t stop until the object of the search is found. By looking in this manner, the person in question can assure that the search will not fail for lack of effort. The phrase “high and low” gets its meaning from the fact that anybody who would see both the high and the low of a location would be leaving nothing unseen.
Certain occasions call for English speakers to use words or phrases that may not have the meanings one would expect, based on the literal definitions of the words. These words and phrases are known as idioms, and they often evolve from their origins to mean something totally different over time. Those meanings are generally understood by everyone in a specific culture. One such idiom meant to convey a thorough search is the phrase “high and low.”
When someone searches in a manner that warrants the use of this phrase, it means that he or she is searching practically every location that is within reach. The reasons for the search can be either serious or frivolous, but it is definitely a meticulous search if the phrase is used. As an example, someone might say, “I’ve been searching high and low for the right pair of shoes for the party, but I haven’t found them yet.”
This phrase also implies that such a search has either been going on for a long time or will continue to go on well into the future. Any search that requires such thoroughness cannot possibly be conducted in a short period of time. The only way it would likely end is if the search results in finding the object or person in question. For example, consider the sentence, “He’ll search high and low until he finds the right person for the job.”
As with many idioms, there is a certain degree of exaggeration that goes along with this expression. Some people go even further with the expression, extending it to say that they will search “high and low and all points in between.” Obviously, it is impossible to search everywhere, but this phrase indicates that there won’t be any slacking in the particular pursuit.