The main difference
A tenant is someone who lives in a property you are renting out in which you dont also live. A lodger is someone who resides in a property in which you also live.
Contracts and agreements
Typically, a tenant has more rights than a lodger. The contract between a landlord and a tenant is called an Assured Shorthold Tenancies (ASTs) - this is the default agreement if you don't specify another type when letting your property. An AST allows the landlord or tenant to end the tenancy after an initial six month period, by giving notice to quit. It's a legal requirement for all deposits taken by landlords using ASTs be protected by a tenancy deposit scheme.
The contract between a landlord and a lodger is called a licence, not a tenancy agreement. Unlike tenants, who require a standard notice period before you can evict them, lodgers can be served 'reasonable' notice to ask them to leave at any point. This is normally 28 days but it could be shorter. As a live in landlord, you should get your lodger to sign a licence in which you set out the conditions of their stay in your property, as well as outlining any house rules, before they move in.
Tenants are entitled to exclude the landlord from their space, which means you should give them notice before you want to enter the property, unless it's an emergency.
Lodgers, on the other hand, can't exclude the landlord from their room so it's important that you don't allow them to put a lock on their door. It's also possible to ask a lodger to move to another room if necessary, though not something you should attempt regularly.
Tenants with ASTs are protected by tenancy deposit protection regulation. Live in landlords with lodgers however are not required to protect their deposits, though they can do so if they choose.
The obligations of a live in landlord are much less onerous than those placed on live out landlords. However, it is necessary for both types to have annual gas safety checks done and have a responsibility to keep the property safe and free from health hazards.