eBGP is External Border Gateway Protocol. This is the version that people are talking about generally. There is also iBGP (interior) is used in much the same way as traditional IGPs.
In recent history there were only 65535 AS numbers that were available (there were actually less as the last 1000 or so were reserved to be used as private AS numbers). This was because the AS was a 2-Byte/16-bit number and that was the maximum that was available. Once the 4-byte/32-bit numbering system was made available it meant that the AS starvation that had been present before was rectified. It also meant that the number of ASs was vastly increased and equal to the number of IPv4 addresses in existence. Due to the unwieldy length of the addresses which can now be created it has become common practice to write the AS numbers down in a format called ASdot which is 2 16-bit numbers concatenated with a dot.
|AS PLAIN||AS DOT|
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