An animated texture is a material whose properties change over time. One example of this is assigning a multi-frame bitmap (for example, an AVI file or an IFL image-file sequence) as a map.
Animated textures can also be materials with keyframed parameters. In addition, in the context of particle systems, a material that uses the Particle Age map or the Particle MBlur map is considered to be animated.
In general, when applying an animated texture to particles in Particle Flow, be sure incorporate it in a Material Dynamic operator.