what is the dress called "tank top"?

I read in the 'American Beauty' script this sentence:

JANE BURNHAM lays in bed, wearing a tank top.

Can any teacher give me an explanation of what it is?

Thanks!

tank top
n.
A sleeveless, tight-fitting, usually knit shirt with wide shoulder straps and no front opening.


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[From its resemblance to a tank suit.]

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Source: The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2000 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.

A Tank top can also be a pullover with a v-neck, no sleeves and usually in rather bright colours, especially stripes. :D