Here's a short story:

Symbiosis (from Greek σύν "together" and βίωσις "living") is close and often long-term interaction between two different biological species. In 1877 Albert Bernhard Frank used the word symbiosis (which previously had been used to depict people living together in community) to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms." 

The definition of symbiosis has varied among scientists. Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any type of persistent biological interaction (in other words mutualistic, commensalistic, or parasitic). After 130 years of debate, current biology and ecology textbooks now use the latter "de Bary" definition or an even broader definition (where symbiosis means all species interactions), with the restrictive definition no longer used (in other words, symbiosis means mutualism). 

Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each other for survival. For example, many lichens consist of fungal and photosynthetic symbionts that cannot live on their own. Others are facultative (optional): they can, but do not have to live with the other organism. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: What has varied among scientists?
Guess: The definition of symbiosis.

Question: What do some believe?
Guess: That it should only refer to persistent mutualisms.

Question: What about others?
Guess: They believe it should apply to any persistent biological interaction.

Question: How else could you describe it?
Guess: Mutualistic, commensalistic, or parasitic.

Question: How many years was it debated?
Guess: 130 years.

Question: What is used now?
Guess: De Bary definition.

Question: By what?
Guess: A broader definition.

Question: What word is being defined?
Guess: Symbiosis.

Question: What language did it originate from?
Guess: Greek.

Question: How was it used in 1877?
Guess: To describe the mutualistic relationship in lichens.

Question: How was it used previously?
Guess: To depict people living together in community

Question: What about in 1879?
Guess: The living together of unlike organisms.

Question: By whom?
Guess: Heinrich Anton de Bary.

Question: What was his occupation?
Guess: Mycologist

Question: Nationality?
Guess: German.

Question: What is obligate?
Guess: Some symbiotic relationships.

Question: What does that mean?
Guess: It means both symbionts entirely depend on each other for survival.

Question: What about others?
Guess: They are falculative.

Question: Meaning?
Guess: Optional

Now answer the following question in the same format.

Question: What does symbiosis mean in other words?

It's the close and sometimes long-term interaction between two species.