Tico is a colloquial term for a native of Costa Rica. The plural form is ticos.
Costa Ricans are usually referred to as ticos by themselves and persons of other Spanish-speaking countries, instead of using the more-formal costarricense. Some dictionaries show the formal name as costarriquenses and also "costarriqueños"; however the latter is seldom used in practice in the modern Spanish Language.
There are two popular explanations of the origin of the term tico. The first is that it derives from the tendency of Costa Ricans to use the -tico diminutive suffix in Spanish instead of the more common and widely-used -ito. Literally -tico, when used as a suffix, in Costa Rican Spanish denotes something very small, as the suffix "-ito" would. Use of "-tico" versus "-ito" depends on the word, as not all of them would be easily adapted to "-tico" suffix. For example "small" is "pequeño", and "very small" would be "pequeñito". In Costa Rica, it would still be said "pequeñito" and not "pequeñitico". However, "chiquito" which may mean "boy" or also a synonym of "small", in its diminutive form will be said "chiquitito" across Spain and Latin America, whereas it will be said "chiquitico" in Costa Rica.
From a linguistic standpoint, the "tico" namesake is not the same as the actual suffix utilized in everyday Costa Rican language. The actual diminutive suffix is actually "-itico", containing an 'i' that changes from the usual 'o' or 'a' in which a word usually ends.
The second explanation of tico is that it's short for Hermanitico (Little Brother in Spanish as pronounced with the suffix as described above.), a friendly and respectful way the people of Costa Rica used in the past to refer to themselves and each other.
In some regions of Mexico (mostly mountainous areas)it is considered a common proper name. loosely translated into English it would be "Todd".