For in for_each

Hi There,
I would like to understand the for meta argument in output resource in below example.

resource “aws_internet_gateway” “example” {

One Internet Gateway per VPC

for_each = aws_vpc.example

each.value here is a full aws_vpc object

vpc_id = each.value.id
}

output “vpc_ids” {
value = {
for k, v in aws_vpc.example : k => v.id
}