Summary from Wikipedia and other places in internet:
3G is a generation of standards for mobile phones and mobile telecommunications services fulfilling specifications by the International Telecommunication Union. Application services include wide-area wireless voice telephone, mobile Internet access, video calls and mobile TV, all in a mobile environment.
4G is the fourth generation of cellular wireless standards. It is a successor to 3G and 2G families of standards. A 4G system is expected to provide a comprehensive and secure all-IP based solution where facilities such as ultra-broadband (giga-bit speed such as 1000+ MiB/s) Internet access, IP telephony, gaming services, and streamed multimedia may be provided to users.
Wi-Fi is a trademark of the Wi-Fi Alliance. It is not a technical term. However, the Alliance has generally enforced its use to describe only a narrow range of connectivity technologies including wireless local area network (WLAN) based on the IEEE 802.11 standards, device to device connectivity.
WiMAX (Worldwide Interoperability for Microwave Access) is a telecommunications protocol that provides fixed and fully mobile Internet access. The current WiMAX revision provides up to 40 Mbit/s with the IEEE 802.16m update expected to offer up to 1 Gbit/s fixed speeds.
Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been used from around 1980 to the present.
Data transfer rates in order from low to high speed:
- 3G: 128Kbps to 384Kbps
- 10BASE-T Ethernet (Wired) 802.3: 10Mbps
- Wi-Fi 802.11b: 11MBps (Max)
- Wi-Fi 802.11g: 54MBps (Max)
- 100BASE-T Fast Ethernet (Wired) 802.3u: 100 Mbps
- Wi-Fi 802.11n: 300MBps (Max)
- 4G: 100Mbps (mobile) to 1GBps (fixed)
- WiMax 802.16m: 40Mbps to 1Gbps
- 1000BASE-T Fast Ethernet (Wired) 802.3: 1GBps
4G and Wi-Fi have almost the same bandwidth. The difference between them is in range. Wi-Fi is targeted to cover low range networks, while 4G was designed to replace high range mobile networks.