Switch Contact Ratings
Switch contacts are rated with a maximum voltage and current, and there may be different ratings for AC and DC. The AC values are higher because the current falls to zero many times each second and an arc is less likely to form across the switch contacts.  BB15AV-FA NKK Switches SW PB SPDT .4VA VERT BRKT BK ESD
For low voltage electronics projects the voltage rating will not matter, but you may need to check the current rating. The maximum current is less for inductive loads (coils and motors) because they cause more sparking at the contacts when switched off. BB15AV-FA NKK Switches SW PB SPDT .4VA VERT BRKT BK ESD
 

Switch Contacts
Several terms are used to describe switch contacts: BB15AV-FA NKK Switches SW PB SPDT .4VA VERT BRKT BK ESD
Closed - on position, contacts conducting, there may be several on positions.
For example: the simplest on-off switch has one set of contacts (single pole) and one switching position which conducts (single throw). The switch mechanism has two positions: open (off) and closed (on), but it is called 'single throw' because only one position conducts.
Way - number of conducting positions, three or more. BB15AV-FA NKK Switches SW PB SPDT .4VA VERT BRKT BK ESD
Momentary - switch returns to its normal position when released.
Open - off position, contacts not conducting. BB15AV-FA NKK Switches SW PB SPDT .4VA VERT BRKT BK ESD
Pole - number of switch contact sets. BB15AV-FA NKK Switches SW PB SPDT .4VA VERT BRKT BK ESD
Throw - number of conducting positions, single or double.