"Logos" can be vaguely translated as "the reason for things". The word "logic" comes from the root word "logos", or "the reason of things". In philosophy, it is defined as the cosmic reason or the cosmic rationality implying an order and intelligibility to all things and events in terms of their value and perfection.
Logos already implies some kind of meaning in the form of rational thought. For the logos, reason and thought already have some kind of privileged significance in describing being and, moreover, the relations of being: logos as the reason, the rationale of the world, the nature of the world.
The logos, in addition to implying this kind of rationale-- this kind of rational mediation of the world principally through words and through language-- is also going to be identified in another way: "logos", by default and upon its inception, implies an exclusion. Logos is by nature exclusionary since, in addition to identifying the reason, the rationale, the meaning behind things-- also says that this reason, this rationale, is its form, is its identity, beyond which there is only nothing and nothingness.
For Heraclitus, and at the outset, "logos" basically meant the consistency of inconsistency and the "identity of difference" by consequence. Heraclitus teaches us that the world is inherently somehow inconsistent every time we try to ground the world or freeze the world into some kind of fixed, idealistic form, let's say a "phenomenal form". This is how Heraclitus arrives at the Notion that the world will necessarily be inconsistent with the "phenomenal form" because it's always changing and always in motion: "No man steps in the same river twice; for it's not the same river and he's not the same man".
It is the permanence of what is impermanent that allows Heraclitus to derive this concept of logos. Logos therefore never entailed, from the very beginning, any kind of substantive being. Logos, from the very beginning, as the beginning of it all, already entailed some kind of consistency of inconsistency alone. The content of logos can only be defined by something which is "not what it is", in contrast to the base, tautological, dogmatic saying "it is what it is".
Heraclitus is also known for arriving at the insight that "all is one" because Heraclitus is dealing with a world that has already been lacerated into distinctions and differences in his thought. So, it is the all of difference, all of these different things that is in the end "one", that "One" for Heraclitus is the one of difference itself. [1]