SP Char in HTTP Headers?

Question

I've been examining HTTP 1.1 specifications and well I saw something like this:

Request-Line = Method SP Request-URI SP HTTP-Version CRLF

I know what this Request-Line stands for but I wonder what SP stands for? What kind of character is that?

Link: http://www.w3.org/Protocols/rfc2616/rfc2616-sec5.html#sec5.1

Edit:

In the hope of helping people who visit this page somehow, I found this complete set of codes in the pages provided by the answering people:

OCTET          = <any 8-bit sequence of data>
CHAR           = <any US-ASCII character (octets 0 - 127)>
UPALPHA        = <any US-ASCII uppercase letter "A".."Z">
LOALPHA        = <any US-ASCII lowercase letter "a".."z">
ALPHA          = UPALPHA | LOALPHA
DIGIT          = <any US-ASCII digit "0".."9">
CTL            = <any US-ASCII control character
                 (octets 0 - 31) and DEL (127)>
CR             = <US-ASCII CR, carriage return (13)>
LF             = <US-ASCII LF, linefeed (10)>
SP             = <US-ASCII SP, space (32)>
HT             = <US-ASCII HT, horizontal-tab (9)>
<">            = <US-ASCII double-quote mark (34)>

They become important as they're being used buy the specifications to explain the formats of the headers and many other things as well.

Answer 1

SP = US-ASCII SP, space (32)

source http://www.w3.org/Protocols/HTTP/1.0/spec.html