A flight reservation is a real hold placed in the airline's system. It carries a verifiable reference and a time limit, and it is not valid for travel.
A ticket is a purchased contract of carriage. It lets you board, and it usually costs far more to change or refund.
For visa purposes, a reservation is normally sufficient because the consulate is checking your plan, not your boarding pass. Always check the embassy checklist for the country you are applying to.
Build a verifiable reservation