A word is smallest meaningful unit of a language in both forms: written and spoken language. A word consists of letters in written language, and sounds in spoken language. From the other side, words build up a larger unit known as: a sentence.
For example:
Stay, up, for, man, the, etc.
Word criteria:
words should be separated in the context by small pauses in order to be understood. The pauses differs from one context into the other. For instance, in the spoken language, words are separated by small pauses that endure less than one second. As for the written language, we separate between words using spaces. There are many types of words known as parts of speech such as: verbs, adverbs, adjectives, prepositions, etc.
There is a word that has more than one meaning. On the other hand, there are different words that have the same meaning.
For example:
My husband is dancing on the stage over there.
( means the dancing floor)
She is in the first stage in the secondary school.
(means the year/ level)
She asked him for a gift/ present.
Hence, the meaning of the word depends upon the sentence and the context in which it exists.