This is the BLOCK constant. This means the compression class will flush every time a new block has been created. A block is a certain amount of data, which size depends on the machine you're using.

This is the FINISH constant. This means the compression class will only do a flush when the compression has been ended.

This is the FULL_FLUSH constant. THis means the compression class will fully flush the stream every time new data has been added.

This is the NO_FLUSH constant. This means the compression class won't flush it's data when the flush setting is set to this.

This is the PARTIAL_FLUSH constant. This means the compression class will only do a partial flush when the flush setting is set to this.

This is the SYNC_FLUSH constant. This means the compression class will only flush if it needs to sync up when the flush setting is set to this. This happens when new data is added to the compression stream.

This is the TREES constant. This means the compression class will only flush the tree. This is a sort of dictionary that is used to compress the data.