It is having information about how the education system works. If a plan is totally linear, but requires other people who are not under the control of the teacher to do certain things at a particular time, it is quite obvious that the lesson can fail if someone doesn't perform as expected. The same idea applies to materials needed for the lesson, but which the teacher must obtain from other sources. If a video, software, hardware, or print materials are needed, but don't arrive on time, the teacher must have an alternative planned that will still lead students to the objective of the lesson. Reticulation is a process that helps ensure that the planned lesson can be implemented as scheduled.
Reticulation is about thinking.
Defined concisely, it is what the teacher actually does in presenting the lesson. Instruction and teaching are virtually the same thing. Instruction is a special form of communication that, in most classrooms, is dependent on feedback to be effective. There is no shortage of information on what constitutes a particular instructional method. What is far more important is the professional knowledge base that provides criteria for when a particular method is appropriate for given content with students at a defined level of development and who have acquired the prerequisites necessary to learn the content.