what is a addon domian

[advarntek]

ok i am not sure what a addon doamin does it mean.
i got to my vodahost cp. i click addo domain. i click new addon domain. i enter lotese.com. and redirect to testdomain23.com does this mean if i enter in my web addres bar. www.lotese.com it will redirect me to testdomain23.com. or i have registered my vodahost domain with the domain name advarntek.co.uk if i add on domain will i have to enter lotese.com.advarntek.co.uk and it will redirect me to testdomain23.com