A spiral is a curve on a plane that winds around a fixed center point at a continuously increasing or decreasing distance from the point.
A helix (a three-dimentional spiral) is a three-dimensional curve that turns around an axis at a varying distance while moving parallel to the axis.
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis.
The length and width of a helix typically remain static and do not grow like on a planar spiral.
The word helix comes from the Greek word ἕλιξ, "twisted, curved".
A conic helix may be defined as a spiral on a conic surface, with the distance to the apex an exponential function of the angle indicating direction from the axis.