What is difference between Joiner and Lookup Transformation

Joiner will join the two different data sources based on a 
join condition ,and pass only the rows which satisfy that 
condition.discards the remaining rows.

Joiner transformation supports 4 types of joins at 
Informatica level
Normal
Master Outer 
Detail Outer 
Full Outer

LookUp Transformation

Lookup transformation basically for Reference,based on the 
lookup condition.when u want some data based on target 
data ,will take lookup on that particular table and 
retrieve the corresponding fields from that table.
we can override the lookup transformation using the SQL 
query.