Hi Nilay,
Marketing list is a list of customer contact details where your customer has opted in or opted out for certain subscriptions for example email newsletters, marketing updates etc..This list can be part of your existing or future campaign. While segment is broad term which signify how you can use existing audience which are part of your "marketing list" or may be "imported" or may be "filtered" to feed your customer journey.
Scenario 1: You have to launch a new email campaign ( to introduce new product ) who are your existing customers living in
central London. In this scenario you will design your segment and pull up customers who are only living in central London.
Scenario 2: You have published a new blog and want to share with subscribed or opt-in audience to receive email notifications. In this scenario you will target the audience which are part of your marketing list "who have opted " to receive email notification.
Hope this helps.
Thanks & Regards
Shubham Dubey
