8MM: 8mm tapes look like Hi8 tapes (see below) but they record only 270 lines of resolution. It is of no professional value (and if you ask me, no consumer value either).
S-VHS (Super-VHS): A marked improvement over regular VHS, S-VHS achieves this quality improvement by recording the luminance and chrominance separately and using 400 lines of resolution. Compared to other formats, S-VHS is still rather low quality, yet it is used rather widely by low-level professionals such as public access or event videography. Note that while S-VHS decks can play regular VHS tapes, regular VHS VCRs cannot play S-VHS tapes.
Hi8: Hi8 produces quality about on par with S-VHS (it also splits the luma and chroma) yet its tape and equipment are usually smaller, making it a more portable format. Hi8 inhabits a middle ground between consumers and professionals, so it never quite caught on with either. It is usually used by small local cable stations or in educational programs, although many places are replacing Hi8 with DV.
3/4" (U-matic): At one time, 3/4" was the standard tape format of broadcast news, yet it was officially discontinued in the 1970's and most places have replaced it with BetaSP. That said, it continues to hang on in environments that couldn't afford or didn't care to upgrade, such as local cable stations, small market broadcast stations, and in corporate video. It has better quality than the above formats, but it is dying a very slow death and it is increasingly hard to find equipment to play 3/4" tapes, so it should be avoided if possible.
Betacam SP (BetaSP): BetaSP has long been the standard format of choice for broadcast work and it is as ubiquitous in the professional world as VHS is among consumers. BetaSP replaced the older Betacam format. It is a component format, meaning that the red, green, and blue signals are recorded separately, yielding better color reproduction and a sharper image. It can also be copied more times than the previous formats before image degradation is noticeable. While Sony (the manufacturer of BetaSP) has very slowly been trying to get people to switch their newer, digital formats, BetaSP is so widespread that it will be many years before it is a dead format.
1 Inch (Type-C): An old and very durable format that uses large, reel-to-reel tape machines. Very expensive, and only found in the upper levels of TV broadcasting.
DV25 (DV): DV25 is commonly referred to (if somewhat incorrectly) as just DV. DV25
has a data rate of 25 Mbps. MiniDV, DVCAM, and DVCPro (D-7) are all DV25
formats. See "DV Specifications" for more information.
Digital 8 (D-8): D-8 uses the same compression scheme as DV25, yet it records it onto a
8mm tape the same size as the analog 8mm and Hi8 format. Thus, D-8 decks can also
play 8mm and Hi8 tapes. D-8 is aimed at consumers, and the only reason to ever use it is
if you already have an investment in 8mm or Hi8.
DV50: DV50 is similar to DV25, except that it has double the data rate and color
sampling. The main supporter of DV50 is Panasonic, who call it DVCPRO50.
Digital-S (D-9): Digital-S is a pro format supported mainly by JVC that is equivalent to
DV50. Digital-S uses tapes that look like VHS and S-VHS tapes, although it offers
vastly improved quality over both of those formats. Some Digital-S decks can play S-
VHS. Now more commonly called D-9, since JVC is trying to move it away from any
VHS connotations implied by the Digital-S name.
Digital Betacam (DigiBeta): DigiBeta has become the de facto standard format for high-
end digital production, and has replaced BetaSP in environments that can afford to
upgrade. It's high data rate and very light compression are what wins people over. Like
other Beta formats, it is manufactured by Sony.
D-2, D-3: These two formats are essentially the same signal, the only
difference is that D-2 records on a 3/4" tape while D-3 uses a 1/2"
tape. These formats (and all the formats following it on this list) are only
used in high end production environments, such as at large broadcast stations.
D-2/D-3 is a composite format (the rest on this list are component). Composite
is usually seen as low quality, yet here the signal is sampled so finely that
it is still a very high quality signal.
D-5: Another extremely high-end uncompressed format. It is supported by Panasonic.
D-5 machines can play D-3 tapes.
D-1: Ultra high-end. D-1 is so expensive that it even many high-level productions don't
use it because of its cost. Its data rate is a whopping 270 Mbps, over ten times that of
DV25. It also can record an alpha channel for transparency and keying (this is signified
by the extra 4 at the end of the color sampling stat).
D-6: D-6 is a HDTV signal recorded on a D-1 tape. I don't know much about this.
D-4: Doesn't exist! The number 4 is unlucky in Japan, and since the major video manufacturers are Japanese companies, no one wanted to develop a format called D-4. Just in case you were wondering.