The basic details of these technologies are as follows (read summary in the end for a short version):
Digital subscriber line is a family of technologies that are used to transmit digital dat over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access. DSL service can be delivered simultaneously with wired telephone service on the same telephone line.
Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line (SDSL). Bandwidth (and bit rate) is greater toward the customer premises (known as downstream) than the reverse (known as upstream). This is why it is called asymmetric.
ADSL2+ extends the capability of basic ADSL by doubling the number of downstream channels. The data rates can be as high as 24 Mbit/s downstream and up to 1.4 Mbit/s upstream depending on the distance from the DSLAM to the customer's premises.
WAN stands for wide area network that covers a much bigger region than a local area network, which could be across a town, a region, a country or the entire world. Though there's no commonly-agreed precise cutoff point between a LAN and a WAN, a WAN tends to use "external" cabling such as a phone network or a cable company's fiber optic network. Unlike a LAN, a WAN is usually owned and operated by a different organization to the people and organizations that use the network to send and receive data. Usually a WAN will have slower data transfer speeds than a LAN.
Summary. xDSL is a family of technology and ADSL is a subset or member of it. The only major difference with Symmetric DSL is that the upstream and downstream bandwidth is different, so its called Asymmetric. ADSL2+ is type of ADSL with higher bandwidth. WAN is your connection to outside world like Internet. WAN link can be xDSL, ADSL or in Business environment can also be PPP lease lines, MPLS lease lines, Serial Link or an E1/T1 or ISDN PRI/BRI line etc.
Hope this help.