“Full sun” means a minimum of six hours (usually at least 8) of sunlight per day. For at least six hours, the sun should be directly shining onto the plants nearly every day of the season. Obviously inclement weather and overcast days are not counted. No artificial shade (trees, buildings, etc) are blocking sunlight from full-sun veggies.
One of the easiest to grow, cukes have very broad leaves, a common trait in many full-sun plants.
These grow better in some climates than in others, but are a popular early spring and late fall harvest.
Most melons need nutrient-rich soil, plenty of sunshine, and at least 3 to 4 months of warm weather. Melons can take up lots of space.
Most types of peppers prefer as much sun as they can get.
Like cucumbers, squash plants have very broad leaves and beg for sunlight. Growing them on a trellis or stand can maximize sun exposure.
Like peppers, assuming plenty of water is available, tomatoes will always take as much sun as they can get.