Segmentation (or rather fragmentation)
Although in some literature you may find the term
segmentation to refer to the process of dividing an IP packet that is bigger than the
Maximum Transfer Unit (MTU) of the link, the correct term is
See @adam86 answer for what segmentation refers to.
Switching is totally different, it refers to the process, performed by devices commonly known as
switch, although the official term is
mac bridge, which transfer (unchanged), an Ethernet frame from a LAN to another LAN.
Mac bridges are defined by the IEEE standard 802.1D
In modern Ethernet networking, switching is performed when a switch receives an Ethernet frame on one of its ports and transfers it to another port on which the receiver is attached.
The switch use the destination MAC address present in the Ethernet frame to select the port to send the frame to.
The term "switching" come from the fact the frame is recopied from one port to another one, by opposition with older hubs which send the frame to all ports (except the one on which the frame was received).