The Effects Framework - Introduction to 3D Game Programming with DirectX 9.0 - page 357

A technique is a particular implementation of a special effect.
Typically, an effect file will consist of several techniques that all
implement the same effect but in different ways. Each implementa-
tion will utilize the capabilities of a specific generation of hardware.
Thus, the application can choose the technique that is most fitting
for the target hardware. For example, to implement multitexturing,
we might define two techniques—one that uses pixel shaders and
one that uses the fixed function pipeline. In this way, users with a
pixel shader-capable 3D card can use the pixel shader technique,
and users with a 3D card that does not support pixel shaders can
still execute the effect in the fixed function version.
A technique consists of one or more rendering passes. A rendering
pass consists of the device states and shaders used to render the
geometry for that particular pass. Multiple rendering passes are
necessary because some special effects require the same geometry
to be rendered several times, each time with different device states
and/or shaders.