This word has at least two different meanings.
really, truly, indeed
Mahal kita talaga.
I truly love you.
Really, truly. So much!
It’s really like that.
Talagang ganyan ang buhay.
Life is really like that.
Non-standard shorthand spelling variation: tlga
A similar Tagalog word is totoo (true).
There is also another, unrelated meaning for the Tagalog word talagá, accented differently. It is usually in conjugated form.
Nakatalaga sa tadhana.
Destined by fate.
(Written in the stars.)
Ang isang obispo ay nagtatalaga lamang ng isang pari sa isang lugar kung ang huli ay sanay na ng wika na ginagamit doon. A bishop only assigns (appoints) a priest to a place when the latter is versed in the language being used there.
A similar-looking but unrelated Tagalog word is dalaga.