A logogram, or logograph, is a grapheme which represents a word or a morpheme (the smallest meaningful unit of language). This stands in contrast to phonograms, which represent phonemes (speech sounds) or combinations of phonemes, and determinatives, which mark semantic categories.
Chinese characters and Japanese kanji are logograms; some Egyptian hieroglyphs and some graphemes in Cuneiform script are also logograms. The use of logograms in writing is called logography. A writing system that is based on logograms/logographs is called a logographic system.
In alphabets and syllabaries, individual written characters represent sounds rather than concepts. These characters are called phonograms. Unlike logograms, phonograms do not necessarily have meaning by themselves, but are combined to make words and phrases that have meaning. Writing language in this way is called phonemic orthography.
More information on the Wikipedia page .