Each signed word is made up of five parameters: handshape, movement, location, palm orientation, and non-manual signals/markers (NMS). Each of the five parameters has its set of primes. They are the smallest units of sign language. Without any of these parameter, you have no sign!
A signed word can result in a different meaning when one of these paramaters (or primes) changes. If a word is pronounced incorrectly, it may distort its meaning like "misspelling" or sometimes meaningless.
Many ASL words have more than one prime of a parameter in a single production. For example, the ASL word mother+father ("parents") has one handshape, one movement, one palm orientation, and two locations.
The handshape parameter has over 55 handshapes. ASL linguists have different counts on the number of handshape primes -- e.g. whether to count a small group of handshapes that have a minor difference. Just like the English language has between 40 and 44 phonemes, depending on what linguists' arguments are.
A change in handshape can result in a different meaning or meaningless one, in the same way that a sound unit changed in one word results in a different meaning. E.g. "bay" to "buy" in English.
ASL words school (left) and impossible (right) both have the same parameters of location, movement and palm orientation but they have different handshapes.
Location, one of the five paramaters in sign language, is where your hand is located. Eg. on your forehead, in the air, on the chest, etc. Location doesn't have its independent meaning. It is part of the sign.
These ASL words apple (left) and onion (right) have the same handshape, movement, and palm orientation, but they have a different location which results in a different meaning.
Movement is one of the five parameters in sign language. It is how your hand(s) moves. Eg. move upward, downward, backward, forward or diagonally, wave, zigzag, etc.
These ASL words airplane and fly have the same parameters except for the movement. The former one has the repeated movement and the latter one has one movement.
Another example is that these ASL words chair and to-sit have the same parameters or primes except for the movement. The former one has one movement and the latter one has the repetition.
Palm orientation, one of the five parameters of a signed word, is an orientation of the hand or palm. Eg. hands being upturned or downturned, facing you, facing away from you, etc.
These ASL words balance (left image) and maybe (right image) have the same parameters: handshape, location and movement, but the palm orientations of these signed words are different.
Clayton Valli, et al. "Linguistics of American Sign Language: An Introduction." Washington, D.C.: Gallaudet University Press. 2005. Pp 17.
Charlotte Haker-Shenk and Dennis Cokely. "American Sign Language: A Teacher's Resource Text on Grammar and Culture." Washington, D.C.: Gallaudet Press. 1980.
Related posts: Phonology.