what's the meaning of "to put it crudely"

It probably means to make a rough approximation of the total picture, kinda like saying, "To put it crudely, pi equals 3 "(instead of 3.14159265....)

The meaning could be either of the two you have suggested, Frankly meaning freely, after the Tribe of Germans who came to rule Europe after Rome who styled themselves, The Free...

One person can say "Making Love" and another can say effing, or bumping the uglies... It is hard to pretty up some acts, like killing, and glorify them for mass consumption; and it is much easier to tell things as they are, risking of course the loss of ones reader in the process... Some times we sugar coat the truth because no one will take it any other way...

One definition could be to simplify whilst at the same time sacrificing some degree of politeness or to simplify to such a degree it may offend an expert in the field but may help someone with limit knowledge in the subject to gain some understanding of what is being said.

That's the way I would use the phrase.

What??? Euphemistically??? The truth hurts, and the truth is communication, but since complete communication, like truth itself is impossible, then why not be nice in what we say, and seek not to give offense??? Just to put it crudely... All communication is crude, rude, and inefficient...Only in the recogition of the weakness of communication do we have a hope of overcoming it...

I think "to put it crudely" carries a bit of a different sense than "to put it roughly". Crude implies to me that there is a little bit of the raunchy involved in the choice of wording: perhaps a bit of sexual innuendo or bathroom humor.

Or just earthiness, although it really could apply to any high degree of simplification e.g. it would be appropriate to say "Pascal's wager, to put it crudely, says we should wager that God exists because it is the best bet."

For me, it is plain-speaking that may offend sensibilities but has to be done for the sake of clarification.

Language that offends clarifies nothing; and that does not mean I am free of guilt in this department... There are some people you want to offend, and some people you want to injure with your choice of words- that you do not care if you hurt... Okay; then assume you are not saying some thing about some subject so much as communicating your hate, or perhaps anger... That would be a good place to be honest because if you offend some one once, you can give up on having a meaningful coversation later...

I give a lot of offense without meaning to... I trample into subjects people are very sensitive about, and because I am all clinical about it, like a scientist of some sort- the fact that they are squirming in mental agony is lost on me... I am just talking, but to them I am doing viviisection on their souls... I lose friends faster than I can be introduced to new just because I am blind to social boundries... I want to know, so I ask... I think I know, so I tell... The fact that the hurt is not intentional is beside the point... I am a bull in a china shop... I am insensitive... But I do not intend crudity and no one should unless they wish to end the relationship... We can dance around murder, rape, mayham and disease... We know how to do it, and often we should... People know what you mean, and that is enough...