A LAN is a Local Area Network. Is basically 2 or more computers communicating between them. Their means of communicating varies, from slow (infrared) to fast (sonnet rings.) In theory, you could have any kind of network topology inside a lan, but the most common nowadays are Ethernet/Fast Ethernet connections between pc's, ranging in speed from 10-100mb/s.
A WAN is a more widespread version of a LAN, with computers located at different sites. You can think of the Internet as a very big, public WAN.
AFAIK, the slowest kind of connection is through infrared ports, then through COMM ports (might be wrong there.)
Then, you have phone modems, with speeds of 14k, 28.8k, 33.6k and 56k(actually 53 I think for real.)
After that, you have ISDN, which is a combination of two special phone lines and gives you 128k.
DSL and Cable are (commonly) around the same speed, ranging from 256kb/s to 10mb/s. Check this link. In theory, if you live in a heavily populated area, with many people using cable around you, it might slow down; however, in practice i have never seen it. Also, cable can reach higher speed. Of course, your provider is going to charge you for this.
A t1 is a specially made line composed of 12 cables, each running at 64kb/s. Thus, you can get such a thing as a Fractional t1, which is only a few of these lines, instead of the 12.
T2: A T2 is a digital carrier facility used to transmit a Digital Signal 2 (DS2) formatted digital carrier signal at 6.312 Mbps. This is the equivalent of 94 voice channels.
T3: A T3 line consists of 28 T1 lines or 44.736 million bits per second (commonly referred to as 45 Mbps). A T3 line can handle 672 voice conversations. T3 runs on fiber optic and is typically called FT3. See also T1.
ATM : Is a dedicated connection switching technology that organises digital data into 53 – byte cell units and transmits them over a physical medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path. The pre-specified bit rates are either 155.520 Mbps or 622.080 Mbps, though speeds on ATM networks can reach 10 Gbps.
OC3 : Optical Carrier 3: an optical fibre line carrying 155mbps; a U.S. designation generally recognized throughout the telecommunications community worldwide.
OC12: An Optical Carrier 12 is a high-bandwidth "pipe" connection to the Internet operating at speeds 12 x 51.84 = 622.08 megabits per second.
Equivalent to approximately 14 T3s.
There is also such thing as a Sonnet Ring (which I thing is the base for OC technology,) but i can't google anything about it. I will check my networking book tomorrow.
This is by no means an exhaustive list; just some of the things that are out there.
BTW, when you have a doubt on what something is, go to google and try