what is the difference between capture filter and display filter?

A capture filter is used to select which packets should be saved to disk while capturing. For capture filters wireshark uses the BPF syntax. BPF is module that runs in the kernel and can therefor maintain high rates of capturing because the packets do not have to move from kernel space to user space when filtering. The things that can be filtered on are predefined and limited (compared to display filters) as full dissection has not been done on the packets.

Display filters are used to change the view of a capture file. They take advantage of the full dissection of all packets. This makes it possible to do very complex and advanced filtering when analyzing a network tracefile.