A word is something spoken by the mouth, that can be pronounced. It is also a collection of letters used together to try to communicate a meaning, and these can also usually be pronounced. A logogram is also a word.
Some words have more than one meaning, for example 'spring' can refer to the season, the device, or a conjugation of the verb. Some words have different pronunciation, for example, 'wind' (the noun) and 'wind' (the verb) are pronounced differently. Some words have different spelling for example 'color' and 'colour', which are both correct. Color is used in American English and colour is used in British English. Some words can be only one letter, for example "a" and "I" in English. Besides English, other languages have their own words.
For example, hello is a word.
A word is the smallest thing which can be said with meaning. This contrasts with a morpheme, which is the smallest unit of meaning but may not stand on its own. A word may consist of a single morpheme (for example: oh!, rock, red, quick, run, expect), or several (rocks, redness, quickly, running, unexpected), whereas a morpheme may not be able to stand on its own as a word (in the words just given, these are -s, -ness, -ly, -ing, un-, -ed).
The meaning of a word can be found in a dictionary.
Word Facts for Kids. Kiddle Encyclopedia.