A unicast is a real-time data transmission from a single sender to one recipient. Examples include a video stream, audio stream, or online presentation shared with a single user over the Internet. It is considered "one-to-one" communication since there are only two parties involved.
Unicasting is often contrasted with multicasting and broadcasting — both of which are "one-to-many" forms of communication. Multicasts send data to a specific set of users, while broadcasts do not have a defined number of recipients. Broadcasting is the most common, while unicasting is the least common.
A unicast is a type of cast — the real-time distribution of content. However, the term "unicasting" is sometimes used to describe point-to-point data transfers, such as a file download, and bi-directional communication, such as a phone call. These are both forms of one-to-one communication, but they are not types of casting.