In computers, case sensitivity defines whether uppercase and lowercase letters are treated as distinct (case-sensitive) or equivalent (case-insensitive). For instance, when users interested in learning about dogs search an e-book, "dog" and "Dog" are of the same significance to them. Thus, they request a case-insensitive search. But when they search an online encyclopedia for information about the United Nations, for example, or something with no ambiguity regarding capitalization and ambiguity between two or more terms cut down by capitalization, they may prefer a case-sensitive search. Areas of significance Case sensitivity may differ depending on the situation: Searching: Users expect information retrieval systems to be able to have correct case sensitivity depending on the nature of an operation. Users looking for the word "dog" in an online journal probably do not wish to differentiate between "dog" or "Dog", as this is a writing distinction; the word should be matched whether it appears at the beginning of a sentence or not. On the other hand, users looking for information about a brand name, trademark, human name, or city name may be interested in performing a case-sensitive operation to filter out irrelevant results. For example, somebody searching for the name "Jade" would not want to find references to the mineral called "jade". On the English Wikipedia for example a search for Friendly fire returns the military article but Friendly Fire (capitalized "Fire") returns the disambiguation page. Usernames: Authentication systems usually treat usernames as case-insensitive to make them easier to remember, reducing typing complexity, and eliminate the possibility of both mistakes and fraud when two usernames are identical in every aspect except the case of one of their letters. However, these systems are not case-blind. They preserve the case of the characters in the name so that users may choose an aesthetically pleasing username combination. Passwords: Authentication systems usually treat passwords as case-sensitive. This enables the users to increase the complexity of their passwords. File names: Traditionally, Unix-like operating systems treat file names case-sensitively while Microsoft Windows is case-insensitive but, for most file systems, case-preserving. For more details, see below. Variable names: Some programming languages are case-sensitive for their variable names while others are not. For more details, see below. URLs: The path, query, fragment, and authority sections of a URL may or may not be case-sensitive, depending on the receiving web server. The scheme and host parts, however, are strictly lowercase. In programming