Switches are used to open/close a circuit.
S1 is a "single pole on/off" switch in the off position.
This is a "2 pole on/off" switch which completely isolates the lamp from the supply in the off position.
This may be important if it is a high voltage supply.
The dotted line indicates that S1a and S1b are part of the same switch "ganged" together and operate simultaneously.
This is a "single pole changeover" switch.
Either lamp 1 or lamp 2 is on.
This is a "2 pole changeover" switch.
The unlit lamp is completely isolated from the supply.
Again S1a and S1b are part of the same switch.
This is a "single pole 5 way" switch.
It can select 1 of 5 circuits.
You can have 2p 5w, 3p 4w etc.
(1) a "normally closed, push to break".
(2) a "normally open, push to make".
(3) both used together to make a "changeover" switch.
This is a "changeover" slide switch.
When operated a-b opens and b-c closes.
Here are assorted switch types. Panel-Toggle-Make before break-Pneumatic-Wafer-Proximity-Light activated-Toggle-Rotary Reed-Pull-Locking-Vane-Interlocking-Rocker-Dimmer-Mercury-Tilt-Microswitch Thumbwheel-Key-Wafer-Slide-Float-Optical-Foot-Thermal-Hall effect