This is a Big Maths term meaning a group of connected mathematical facts. Understanding fact families is really useful, especially when dealing with algebraic questions (where there is a missing number in the question). To illustrate this using a simple example, if you were asked 3 + ? = 10, you could work out the missing number by creating the fact family, ie 10 - 3 = 7 so 7 is the missing number because it fits into the fact family.
3 digits + 3 digits
2 digits divided by 1 digit.
This is the more formal method of column addition. A firm understanding of place value is essential.
An extension of simple fact families. Understanding how to generate these fact families from simpler ones, is a particularly good strategy to have especially when tackling division problems using the 'chunking' method, when the numbers we are dealing with get bigger! See division of 3 digits by 1 digit for more information.
2 digits + 2 digits