What technique is used to blend different hair lengths smoothly?

The technique known for blending different hair lengths smoothly is tapering. Tapering involves gradually shortening the hair length from the top of the head to the nape of the neck or around the ears, creating a seamless transition between various hair lengths. This technique is commonly used in haircuts to achieve a polished and uniform look, particularly in styles where a smooth gradient is desired.

While layering, thinning, and texturizing are also valuable techniques in haircutting, they focus on different aspects of hair management. Layering creates varying lengths throughout the hair to add volume and movement, but it does not necessarily focus on blending lengths specifically. Thinning is utilized to reduce bulk and weight from thicker hair types, which can also lead to a more manageable style but does not inherently address the transition between different lengths. Texturizing is aimed at reducing uniformity and creating dimension within the hair, again not directly focusing on the transition of hair lengths.

In contrast, tapering specifically addresses the blending of different lengths in a way that facilitates a smooth and continuous appearance, which is why it is the correct answer for this question.