inbound calling means calls those are received by the 
customer care executive.outbound calls means calls those 
are made by the customer care executive.

Inbound:-Is an part of call center industry where in calls 
comes in and we have to greet customers or solve their 
problems. Most of the customer care processes are inbound.
Outbound:-Where calls go out. Most of the sales and 
marketing calls centers are based on outbound model.

a inbound call center is a place where you will be 
receiving calls from customers

a outbound call center is a place where you will be 
making calls to the prospected customers

First of all it is clear from the word "calling" that you
have to talk to your customers, either you make a call to
them for knowing about their response to your products or
may be to promote and make them aware of your plans and
several schemes.
Inbound Calling- This category of calling explains that the
customer use to make calls to the company's help or enquiry
desk department that is so called BPO's so as to clear their
problems or get any help they want with respect to the
company's product's and manufactures or any offers of the
company they are interested in.
Outbound calling- This category of calling explains that the
company's or the Firm's representatives or call executive's
make calls to the people(doesnt matter that the person they
are calling is attached to the company from any source) and
make them know about their plans and schemes they want them
to be associated or enjoy with.Hence here the company call
executives makes calls to peoples for a promotion or
advetisement of there product and offers..Sales and
marketting are the base of outbound calling..