No. A star usually has lines which cross one another; a decagon does not.
Decagon
it's a decagon.
decagon
A decagon
decagon
A star on a American flag
That depends. What most people describe as a typical star has 5 points with 2 sides to each point, which would be 10 sides. In that case, yes, it would be a decagon.
In 2-d, the naming of polygons is such that a 10 sided shape is a decagon. Even if it is a 5-pointed star shape, it is a decagon. A concave decagon (rather than convex) but still a decagon. In 3-d, a decahedron, possibly, with the term "sides" being used for "faces".
One of the most common answers is a five-shaped star.
There are a number of polygons that are similar to it but if you mean things that look like decagons than nonagon, undecagon, dodecagon, and octagon.
It depends on whether or not the decagon is a perfect decagon or a complex decagon. However, a perfect decagon has no acute angles.
decagon