Wordsearch

Wordsearches are a type of word puzzle involving a grid of letters in which a series of words can be found going in various directions. Despite their simple appearance, wordsearches are a relatively recent invention, only showing up for the first time in 1968.

Background
The origin of the wordsearch is somewhat disputed, as while it's widely considered to have been first published in English by Norman E. Gibat in 1968, it is possible that the puzzle was published earlier in other languages, or patented earlier in English. Of particular note are Pedro Ocón de Oro, a Spanish puzzle maker who worked for multiple Spanish-language publications throughout the 50s, 60s, and 70s and published something called "Sopas de letras" in the 1970s; and James Patrick Carr, a faculty member at the Villa Grove High School in Illinois who may have attempted to patent the word search under the name "Slate R Straight", only to have the idea swiped by the patent company.

Regardless of where the true origin lies, Gibat's wordsearch was first published in the Selenby Digest, a small publication distributed in Norman, Oklahoma. According to Norman, the goal was to create a puzzle that could be solved in line at a supermarket, hence the choice of publication source. The original puzzles also were locally-themed, as the first two had word lists consisting of Oklahoman cities and Norman's street names, respectively. As the idea grew in popularity (particularly among teachers who saw it as a good resource), an unknown individual sent the idea in to a higher-level publisher for syndication.

Puzzle Application
While a traditional wordsearch consists of a square grid, a list of words to find, and the expectation that words are found in one of the eight orthogonal directions, these "rules" are often broken for the sake of a more interesting puzzle, particular when it comes to hunt puzzles.

Hidden Messages
One thing that is much more common in hunt puzzles than any other type of word search is the inclusion of hidden messages only viewable after the puzzle is solved. The most well-known (and most well-used) way to hide these messages is by having the unused letters from the puzzle spell them in reading order. This also allows for the setter to provide hints to observant solvers towards the general area of missing entries, as spotting the message before the puzzle has been completely solved will inevitably show which letters still need to be used up before the message is the only thing remaining.

Other less-common-but-still-documented ways of presenting a message include having entries reading in a particular direction either spell out a message via the entire words/first letters, or having a message spelled out via letters at word intersections.