I think informally, they have the same meaning.
However, the phrase "a lot" refers to an indeterminate unit of measure (which may in certain contexts actually be determinate, e.g. land measurements).
So, technically, "lots of" should be more than "a lot of", since the latter refers to a single unit of measure, and the former refers to multiple units of the same measure (if used in the same context).
The ledger is the collection of accounts.
Ledger and accounts relate to standard accounting practice.
You first record any business transaction in a journal, which is a book or the electronic equivalent of a book. This leaves transactions in simple chronological order. The information recorded includes the date, amount, description, and two accounts. The accounts are identified by number, and their purpose is to categorize the transaction.
For example, suppose you pay a debt. One account categorizes the transaction according to which debt it is. The other account categorizes the transaction by the source of currency with which you paid it, such as a checking account.
Every journal entry is then copied to a ledger, which is a second book organized not chronologically but by account number. The entry is copied twice, so that it is listed under both account numbers in the ledger.
Best Answer
"Plenty" is more about relative quantity. Regardless of the absolute quantity of friends/money/time/whatever, it's enough for what you need. Whereas "a lot" is a statement about a large absolute quantity without a judgment on the value of that quantity.
E.g.:
Me: I have fifteen dollars to spend on this dinner.
You: Oh, that's plenty. (meaning: more than enough money for what you intend to do with that money)
vs:
Me: I have five hundred dollars to spend on this trip.
You: Oh, that's a lot of money. (meaning: that's a large amount of money in absolute terms, but I'm making no statement as to whether it'll be enough for your needs)