This is the size of the AES key. AES is a symmetric algorithm and 128 bit are still considered solid there, although the trend is moving towards 256 bit.
What we're talking about here is the key size of RSA, which is an asymmetric algorithm. If you don't know the difference, go find a basic crypto tutorial. As you can read above, 1024 bit RSA is probably borken. I wouldn't trust 2048 bit too much as well. Also, progress in breaking RSA is happening a lot faster than with AES.
In the context of SSL, an assymetric algorithm like RSA is used to exchange symmetrc keys, which are used afterwards.
That said, 256-bit isn't really that much of an improvement for AES - its favored since that's the US standard for Top Secret classification, but in practice any attack which brings down AES-128 will almost certainly get AES-256 as well. I've switched most of my SSH servers over to default to 128-bit AES ciphers since the difference in difficulty seems small enough that it won't matter if someone actually tries targeting it and can succeed.
In the context of SSL, an assymetric algorithm like RSA is used to exchange symmetrc keys, which are used afterwards.