Certain they'll explain technology used internally (8)
I believe the answer is:
definite
'certain' is the definition.
(similar in meaning)
'they'll explain technology used internally' is the wordplay.
I cannot quite see how this works, but
'technology' could be 'it' (Information Technology) and 'it' is present in the answer.
'explain' could be 'define' (I've seen this before) and 'define' is found in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for definite that I've seen before include "'Certain, beyond doubt (8)'" , "Certain, decisive" , "Clearly decided" , "The is the article" , "Clearly marked out" .)