For additional meanings of "Anomaly", please see Anomaly.
An anomaly is a broad term for an irregular phenomenon. Any object or event which deviates from what is ordinarily expected - whether it is in space or within a humanoid body - can be called an anomaly.
The Bajoran wormhole was known as "the anomaly" to the Jem'Hadar. (DS9: "The Jem'Hadar")
According to Lieutenant Jadzia Dax, an anomaly could be so small that sensors couldn't detect it. (DS9: "If Wishes Were Horses")