Definition - What does Stream Cipher mean?
A stream cipher is a method of encryption where a pseudorandom cipher digit stream is combined with plain text digits. This pseudorandom cipher digit stream is applied to each binary digit, one bit at a time. This method of encryption uses an infinite number of pseudorandom cipher digits per key.
Stream cipher is also known as state cipher.
Techopedia explains Stream Cipher
A stream cipher encrypts an arbitrary length of plain text, one bit at a time, with an algorithm that uses a key. For this form of encryption to remain secure, its psuedorandom cipher digits should be unpredictable and the key should never be used more than once. The pseudorandom cipher digits are generated through a number of random seed values that use digital shift registers. The encryption of each digit is dependent on the current state of the cipher, warranting the name state cipher for this. RC4 is a popular stream cipher that is widely used in software.