Glyphs
It is a rendering feature.
This is a geometry displayed one some points of the dataset. This geometry can be anything (see Glyph with custom source) and can be modified (oriented and scaled) following the data at the corresponding point. So indeed, you can have at each point an arrow oriented as your vector, with a norm proportional to your vector.
StreamLines
It is a mathematical construction.
This is a set of continuous lines that goes through the data set, following the vector field.
Because of the mathematical interpolation, this more costly than the glyphs