What is the use of .htaccess file in asp.net application ?

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ASP.NET

I have a .htaccess file in root filder of my application and something is written like this in that file

RewriteRule ^(/eyewear/([A-Za-z]+)(.+)(-eyeglasses|sunglasses).html)$ /eyewear/product.aspx [NC]
RewriteRule ^(/eyewear/([A-Za-z]+)(.+)(-contact_lens).html)$ /eyewear/contactlens_product.aspx [NC]
RewriteRule ^(/eyewear/([A-Za-z]+)(.+)(-rxsunglasses).html)$ /eyewear/rx_product.aspx [NC]

I am not getting what is it and what is its use..??
Plzzz help