The Lasso tool allows a selection to be made by drawing a freeform outline. This tool is useful for selecting with gesture-like motions, and to follow contours.
In the toolbox, the Lasso is grouped with the Polygonal Lasso and the Magnetic Lasso
- Selection tool common controls
Like the Brush, the Lasso can be used in a segmented mode by holding down Alt/Option. While using the modifier key, clicking will designate an endpoint for a new segment; releasing the modifier key will complete the selection. This is similar to the function of the Polygonal Lasso.
- Pen, which can make similar freeform regions by use of paths
- Lasso tool at the Photoshop Wiki