In reference to a company sharing information that it has collected about a customer, what is meant by “opt in”? By “opt out”? In your opinion, which of these is preferable?

In reference to a company sharing information that it has collected about a customer, what is meant by “opt in”? By “opt out”? In your opinion, which of these is preferable?

In reference to a company sharing information that it has collected about a customer, what is meant by “opt in”? By “opt out”? In your opinion, which of these is preferable?
In reference to a company sharing information that it has collected about a customer, what is meant by “opt in”? By “opt out”? In your opinion, which of these is preferable?