What does having a trace of leukocyte esterase urine mean?

Usually normal. Leukocyte esterase released by lysed neutrophils and macrophages is a surrogate marker of the presence of white blood cells (WBCs). Leukocyte esterase suggests that there are white blood cells in the urine. Trace means few WBC produced small amount of leucocyte esterase.
Some bacteria. this is a byproduct of some bacteria in urine trace means you only have an insig amount of bacteria in urine and you dont need to worry abt it.