"Radial" parts in the context of electronics typically refer to through-hole components that have leads protruding from the bottom or one side of the component, generally aligned along a single axis. These components are often mounted vertically on the PCB (Printed Circuit Board).
The term "radial" comes from the way the leads radiate out from the body of the component.
Common examples of radial parts include:
•Radial Electrolytic Capacitors: These are often used in power supply circuits due to their high capacitance and voltage ratings. They have a cylindrical body with two leads coming out from one end.
•Radial Inductors: These are commonly used in filter circuits and power electronics. Like capacitors, they have a cylindrical body with two leads coming out from one end.
•Radial Leaded Ceramic Disc Capacitors: These have a disc-shaped body with two leads coming out from one end.
One of the benefits of radial parts is that they can help save space on the PCB because they can be mounted vertically. However, they do increase the overall height of the board, so design considerations need to be made if space is a concern.
As always, for specific information such as lead spacing, physical dimensions, or electrical characteristics, refer to the manufacturer's datasheet for the specific component in question.
To create a Radial part click the 
button in The Part Builder
The part builder will automatically create the footprint for the device and also a suitable schematic symbol with the pin names left blank for you to fill in.