write-back与write-through什么意思？

看一篇英文文档，写MMU时，有这样一句话，“write-back or write-through data caching”不明白什么意思？ :(

但是有人这样贴：
write through: upon write, update data in cache and at the same time, update data in memory.
write back: upon write, update data in cache, and flush the data into memory when the cache line is to be replaced, or flush cache instructions are executed explicitly.

楼上好像跟这个意思相反，到底那个对呀？