Anomalies are oddities present on some uncharted planets in Mass Effect 2. An anomaly indicates the presence of an available assignment on that planet (the only mission that is associated with an anomaly is Jacob: The Gift of Greatness).
If a planet has an anomaly, EDI will inform you that she has detected one when you enter the planet's orbit. In order to locate the source of the anomaly you must scan the planet. When you scan the planet, the targeting reticle will contain a white line pointing in the direction of the anomaly. When the targeting reticle gets sufficiently close to the source of the anomaly a white dot will appear on the map marking the anomaly's location. Launch a probe towards the white dot in order to unlock the assignment; doing so will enable you to land on the planet.