1. A shorthand acknowledgment that the speaker is aware of the preceding statement in a conversation, and has discerned the meaning of the statement.

Usually, this is an emotionally neutral phrase.

Usually used in writing, such as email, and may be followed by a period ("Understood.") depending on personal preference.

Synonym of Noted, and is normally acceptable in Business English. A more formal equivalent of gotcha, which is normally not acceptable in Business English. Compare: affirmative, correct, OK, right.

2. A disingenuous acknowledgment of a preceding statement in a conversation. This secondary definition usually occurs when the speaker is obligated to reply to a statement contrary to the desires or expectations of the speaker, but would be reprimanded for an explicitly negative or contrary reply.

In short, a common way to implicitly disapprove of a statement by neither explicitly permitting it nor praising it.

This secondary definition is highly dependent on plausible deniability, and may be misunderstood by the recipient.
If the implication is understood, the recipient may take offense, as it displays disobedience on the part of the speaker.

It means understandable but if you are trying to take the piss out of someone at the same time.

to understand somebody, commonly used as a question

the fuck that goes in the middle of words

much like the understood "k" in knife or knights

When you need to make it clear you got it the first damn time they said it.

When only people from the hood will understand.

this refers to a very smart female sheep, but it should be used as an insult for a know-it-all who happens to be a female sheep.

A phrase used when someone is giving it 110%

Weather it’s what they’re doing, what they’re wearing, someone who is really on top of their shit

When the implied task of let's have sex is understood