Glossary » case sensitivity
whether an application distinguishes between phrases based on whether the letters are upper case or lower case. If the distinction is relevant, then the system is case-sensitive. Otherwise, it is case-insensitive.
In search engines and in search-and-replace systems, case insensitivity is often the default. Thus, if you type “hci,” you will still be able to find the word “HCI.” Sometimes however, you’ll prefer to set the system to be case-sensitive, for instance, when you want the country “US” to be distinguished from the pronoun “us.”
Another common domain in which case sensitivity is relevant is command-line interfaces and programming languages.