Where is the 'line' drawn?

[GobyGuy5]

Freshwater/Brackishwater/Marine

At what salinity is water considered FW, BW or MW?
The reason I asked this is because when I researched the knight goby, I found that it prefers Freshwater, however, It also cannot tollerate PURE freshwater, and requires some salt (around 1.001-1.005 specific gravity) so, I was wondering if this salinity is considered brackish or fresh, and where the drawing line is, I understand the drawing line for Brackish and Marine to be 1.020-1.025, so what about freshwater and brackish water?

Many people add some 'aquarium salt' to their aquariums, but that doesn't make them BW, so the term 'somewhat salty' is a little too vague...........

[olaf]

Freshwater is from 1.000 to 1.005, brackish is from 1.005 to 1.018, and marine is from 1.018 and up.
Knight Gobies in mangroves encounter everything from freshwater all the way to marine. They are best kept in slightly brackish to full brackish. I had a breeding pair of Knight Gobies and the salinity of the tank would range from 1.005 all the way to 1.018 depending on the time of the year. Doing this salt content change, I would see the different types of fish go into their breeding colors and behaviors and breed. None hatched since it is a community tank the eggs would usually get eaten (the puffers - those lil piggies).
Fish that bred.
Bumble bee Gobies
Chromides
Knight Gobies
Red Scat - the scat died because of egg impaction

[RTR]

FW may be hard, but it should not have salt. If it has salt and measurable specific gravity above 1.000, it is brackish IMHO. So for me brackish is from 1.001-1.019 sp. gr. You can sudivide that range into light, medium, and high brachish as you wish.

[VoodooChild]

I've read in a few spots that the definition for brackish is one fourth of what you would find in true seawater. Therefore a gravity of 1.006 or so.