Pure public goods

Not normally provided by the private sector

Because they would be unable to supply them for a profit

Quasi public good

A near public good

It has many but not all characteristics of a public good 

Quasi public goods are 

Semi non rival 

Up to a point 

For example more consumers using a park reduces the space available for others

Quasi public goods are also

Semi non excludable

It is possible but difficult or costly to exclude non paying consumers

For example fencing a park or beach and charging an entrance fee

Free rider problem

Means that once a public good is provided it is impossible to stop someone from benefiting from it even if they havent paid towards it