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"Happy birthday" is a phrase which is often translated as "feliz cumpleaños", and "my son" is a phrase which is often translated as "mi hijo". Learn more about the difference between "happy birthday" and "my son" below.
happy birthday( 
hah
-
pi
buhrth
-
dey
)A phrase is a group of words commonly used together (e.g., once upon a time).
1. (general)
a. feliz cumpleaños 
So, you're 18 today! Happy birthday!¡Así que cumples los 18 hoy! ¡Feliz cumpleaños!
my son( 
may
suhn
)A phrase is a group of words commonly used together (e.g., once upon a time).
1. (my child)