Thank you for your question, my name is Richard.
It means that you are referencing a field that has the same names in two tables.
So for instance,
select orders from order, otherorders
Orders is in both so it will error. You need to do it as
select order.orders from order, otherorders.
This means you specify in your query exactly where it comes from.
If you have any difficulties at all, please do not hesitate to let me know so I can assist you further