Ideograms are symbols that represent an idea in a written language, as opposed to using phonemes or syllables to construct words. An ideogram is distinguished from a pictograph in that a pictograph is any symbol that represents an idea, whereas an ideogram is part of an established written language. Ideograms are used in such languages as Chinese and Japanese (although Japanese use their ideograms extensively for their pronunciation as well.) Early hieroglyphics and cuneiform were also ideograms, though later they were used extensively (and in cuneiform, exclusively) for their pronunciation. Ideograms are said to represent concepts rather than words because often an ideogram can be pronounced differently depending on the context.
An interesting question is how one uses a dictionary for a language that uses ideograms. In Japanese, for example, where ideograms are called kanji, each ideogram is made up of one or more "radicals". A radical is a very basic ideogram, representing a simple concept, like "man," "sun," or "tree" for example. When looking up a kanji, one must be able to isolate the important radical from the ideogram using a system. Then one counts how many additional strokes there are in the ideogram, in addition, to the radical. A Japanese kanji dictionary is arranged by radical first, then additional line or brush strokes. Therefore, one finds a definition, by looking up the kanji by radical plus additional strokes. For example, a particular kanji may be composed of the radicial for "man," and 7 additional strokes. To look this up one finds the radical for "man" in the dictionary and then passes through 1 additional stroke, 2 additional strokes, etc. until one finds entries for 7 additional strokes.The entry will be found here with a definition. To assist the user, there is often an index for the radicals at the end of a kanji dictionary.