bosom friend，親密的朋友，知心知己的朋友。
He is one of my bosom friends.
他是我的知己。
Within the Four Seas，四海之內。
Within the Four Seas means
within the territory of China.
The ancient Chinese thought
China's territory was surrounded
by the Four Seas.
四海之內，即古代中國疆域以內。
If you have a bosom friend within
the Four Seas, even at world's
end he remains close to you.
海內存知己，天涯若比鄰。
If you drink with a bosom friend,
a thousand cups are too few.
If you argue （爭吵）with a man, half a sentence is too much.
酒逢知己千杯少，話不投機半句多。