A rotational ambigram is a word written to say the same word when inverted. If the word says crystal, the artist could find a clever way to make it say crystal when turned upside down.
A bilateral mirror image ambigram is a word written to say the same thing from left to right and right to left. If the word says crystal, the artist may find a way to make it say crystal backwards.
A symbiotogram is word written to say two words. At first, it appears to be one, but--when flipped or read in the other direction--there is different word. When read in one direction, the word could say queen; when flipped upside down, it might say king.
Two words written as a figure/ground relationship say one word in black and the other word in white. It does so saying the first word in regular black print. The second can be seen if you study the white space between the letters of the first word. The white space between letters of a word is called negative space. The word may say queen in black. However, if you stare at the negative white space, it will say king.
Logos place the name of a company, business, sports team or establishment with a picture or design around the name. A good logo is memorable and fits the name or the nature of the company. Unlike the other types of word art, a logo must be easily read upon first glance.