Case is a typographical phenomenon that, fortunately, affects only a few scripts, the so-called bicameral ones: Latin, Greek, Coptic, Cyrillic, Armenian, liturgical Georgian, and Deseret. We say "fortunately" because there is a complex problem that makes the processing of textual data more difficult.
Unicode distinguishes three cases: lower case (the "small letters"), upper case (the "capital letters"), and title case (the case of characters that are capitals at the beginning of a word). The name "title case" is very ill chosen, as this concept has nothing to do with titles, at least as they are typeset in most languages. This name comes from the English-speaking countries' custom of capitalizing all the important words (including the first and the last) in titles: what is "La vie est un long fleuve tranquille" in French becomes "Life Is a Long and Quiet River" in English.
Before describing the properties that pertain to case, let us note, by way of information, that four cases still are not handled by Unicode:
Obligatory lower case. These are letters that remain in the lower case irrespective of the context. Example: German has the abbreviation GmbH (Gesellschaft mit beschränkter Haftung = 'limited liability company'). In this abbreviation, the letters 'm' and 'b' must always be written as lowercase letters, even in the context of full capitals. Another example: if "mV" stands for millivolt and "MV" for megavolt, we had better treat the 'm' ...