Confused about FLINK task slot

The answer might come late. But:

A Taskmanager (TM) is a JVM process, whereas a Taskslot (TS) is a Thread within the respective JVM process (TM). The managed memory of a TM is equally split up between the TS within a TM. No CPU isolation happens between the slots, just the managed memory is divided. Moreover, TS in the same TM share TCP connections (via multiplexing) and heartbeat messages. They may also share data sets and data structures, thus reducing the per-task overhead.

Source: https://ci.apache.org/projects/flink/flink-docs-release-1.5/concepts/runtime.html#task-slots-and-resources

Each worker (TaskManager) is a JVM process, and may execute one or more subtasks in separate threads. To control how many tasks a worker accepts, a worker has so called task slots (at least one).

https://ci.apache.org/projects/flink/flink-docs-master/concepts/runtime.html#task-slots-and-resources

@Janukowitsch's answer is good. Additionally, a TS represents a fixed subset of resources of the TM. One TS can take more than 1 thread. Actually one subtask/task is executed by one thread. Multiple subtasks/tasks can be deployed in the same slot.