I am assuming you are talking domestic construction.
Open your ceiling access panel and have a peak at the roof framing system. If it is a truss system the chances of your internal walls being load bearing are small as these tend to be designed to span from external wall to external wall, thereby freeing up the internal space for more elegant internal layouts design.
If you see a traditional framing system you will see rafters with collar ties and struts bearing off certain internal walls. Generally these strutts will be anchored to a central wall running the length of the building, but may also be bearing off others. You should be able to effectively determine whether the wall you want to remove is strutted or not. If it isn’t, then there is a good chance it isn’t loadbearing.
If in doubt, consult your Engineer or Builder.
There are several easy ways to identify a loadbearing wall. The one’s that work for me:
Look for jack posts in the basement – these line up with load bearing beams/walls which carry loads from 1st and 2nd floor levels.
The thicker the wall, the more likely it is a loadbearing wall (regular wall is 4 ½" thick unless 5/8" drywall used
if the span is greater than 14'6" and conventional lumber was used, chances are the joists or trusses above need to be supported by a wall as they will ‘match up’ with other joists part way across the room within the ceiling.
Look in the attic and see where the trusses cross. Where they cross or match up needs to be supported
Check with an engineer or contractor, or look at your house plans if you have them