what does ' one love' mean in English?
I heard 'one love' is not only means a kind of love, but also means 'bye-bye' in slang.Is it true? thank you.

Question

Answer

As a Jamaican, I can tell you that if we say 'one love' it can mean 'bye', 'peace' etc.  I think it became popular through Bob Marley's song 'One love'.

'One love' when used in sports means that the score was 1-0.  So the team that lost (got '0') got 'one love'

Answer

it comes from american hip-hop taste.
as Alipetgis mentioned, we say that end of the convasation. 
`peace out` `one love peace` `one love` etc,.
it is bye, also sharing our mind. sharing we have same mind or taste.
but it is not for everybody, somebody `share` same flavor.
MV by Nas `One Love`
http://jp.youtube.com/watch?v=hrngXKmJXAY&feature=related
this will give you the flavor :D