Difference between a target group and segment?

Hi experts,

I´m very new at the topic "CRM Marketing" and currently reading some material (wiki, book, etc) regarding Marketing and trying to understand the elements and processes. Could someone please tell me the difference between a target group and a segment? What is used in the other? How do they work together? What have to be created first? Is it right that a target group are the business partners and the segment is collection of filters?

Thanks in advance!

Regards,

Anna