Complex sentence: In mathematics, a spline is a numeric function that is piecewise-defined by functions such as polynomials, and which possesses a high degree of smoothness at the places where the polynomial pieces connect (which are known as "knots").
Split into simpler sentences: In mathematics, a spline is a numeric function that is piecewise-defined by functions such as polynomials. They often possesses a high degree of smoothness at the places where the polynomial pieces connect (which are known as "knots").