There are 4 standard formats:
DVD-5 holds 4.7GB and is supported by the DVD+R/RW and DVD-R/RW formats. It is also known as Single-Sided Single Layer.
D10 and D18 are not as common.
DVD-5 is an acronym that means a DVD disc that is one-sided single-layer disc and can contain upto 4.38 gigabytes of data on it.
A DVD-5 (single sided) DVD-Video disc will hold nominally 133 minutes of high quality MPEG-2 encoded video, together with three surround-sound audio channels and four subtitle channels. (Without video compression one DVD-5 disc would hold only about 3 minutes of video).
One form of DVD discs that means a single-sided dual-layer DVD disc. DVD-9 can hold approximately 7.95 gigabytes of data.DVD-9 DVD-Video discs are problematic for DVD-R owners, because the cheap, writable single-layer DVDR discs can only hold the same amount of data that DVD-5 discs contain, due technical reasons. However, there are several ways to copy a DVD-9 disc to a standard, single layer DVD-R or DVD+R disc.
DVD-9 is nowadays often used as the marketing term for dual layer DVD-R and DVD+R discs and use of that name is quite appropriate as the dual layer recordable discs can hold exactly the same amount of data as "pressed" DVD-9 discs can.