TLS (Transport Layer Security) is an Internet protocol formed within IETF to develop an Internet standard that will replace SSL v3.0. The TLS protocol provides communications privacy over the Internet and allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery.

The TLS protocol is based on the SSL 3.0 protocol specification as published by Netscape. The differences between TLS 1.0 and SSL 3.0 are not dramatic, but they are significant enough that TLS 1.0 and SSL 3.0 do not interoperate (although TLS 1.0 does incorporate a mechanism by which a TLS implementation can back down to SSL 3.0).
 

Differences between SSL v3.0 and TLS v1.0:
When using a cipher block algorithm, data application should be a multiple of the cipher’s block length. Therefore the data to be encrypted is padded out to be in a proper length.
In TLS, the padding can be any amount that ends in a total length that is a multiple of the cipher’s block length (up to 255 bytes).
For instance, if data before encryption is 79 bytes long and the cipher’s block length is 8, then the padding length can be 1, 9, 17, and so on, up to 249.
In the earlier versions of SSL, the padding length had to be the minimum amount required so that the total size of the data would be a multiple of the cipher’s block length, so if we look at the example above, the padding length would have to be 1.
Using a variable padding length makes it more difficult to attack by analyzing the exchanged message’s length.
TLS supports all SSL v3.0 alert messages except the no_certificate message and in addition has other new alert messages. TLS also supports all of the SSL v3.0 key-exchange and cipher algorithms with the exception of the Fortezza key-exchange and symmetric encryption algorithm.
There is a minor difference between the versions in the MAC computation, but the level of security is about the same in both of them. There are also some small, insignificant differences in the certificate_verify and the finished messages, which we will not elaborate on here.

After the IETF published it as an Internet standard, the TLS protocol has been universally accepted on the World Wide Web for authentication and encrypted communication between clients and servers.

Remark: This site is mainly about SSL version 3.0, which is very similar to SSL version 3.1.