What does こと do in these sentences?

Question

This is an excerpt from a mail my language partner wrote me. For some context: 年末はいろいろと忙しいと思いますので、無理しなくていいですよ。 昔の呼び方で、12月のことを「師走（しわす）」と言います。「師（し：先生のこと）も走り回るくらい忙しい月」という意味ですよ。 それに日本では、忘年会（ぼうねんかい)シーズンです。 忘年会とは、その年の苦労を忘れるために行う宴会（えんかい：party）のことで、職場の人と飲みに行くことが多いです。友達同士でも忘年会をするので、私の主人は、12月に４回も忘年会に行きます。

The sentence in question: 忘年会とは、その年の苦労を忘れるために行う宴会（えんかい：party）のことで、職場の人と飲みに行くことが多いです。

My attempt at translation: "About the year-end-party, Out of the parties one performs to forget the worries of the year, there are many to go to to drink with people of the company."

So, first I don't know wether my interpretation of で in のことで is correct or not. I interpreted it as the abbreviated form of のなかで, because if I interpreted it as a location marker, the interpretation I could've come up with didn't make much sense anymore: "...at the parties one performs to forget the worries of this year, there are many to go to to drink with people of the company."

I'm also a bit unsure about the way I interpreted ことが多い, since I'm not 100% sure wether the こと references back to the parties or not.

Ultimately, 忘年会とは. I don't really know what to do with と. If I just interpreted it literally, it would work somehow: "With the year-end-party,(it is like that...)" But I have no idea wether this applies here or if it would be a legit approach at all...^^

Answer 1

Ａ：忘年会とは、その年の苦労を忘れるために行う宴会のことで、職場の人と飲みに行くことが多いです。

"とは" in "忘年会とは" means "means, indicates or is", so "XとはYです" is translated as "X is Y", "X means Y" or "X indicates Y".
jisho.org here difines とは as

particle indicates word or phrase being defined​

"ことで" in "宴会のことで" is "ことであって" or "ことです。そして".

So, A is interpreted as B.

Ｂ：忘年会とは、その年の苦労を忘れるために行う宴会のことです。そして、忘年会とは職場の人と飲みに行くことが多いです。

"忘年会とは職場の人と飲みに行くことが多いです" in B is not natural, so I rewrite it as C.

Ｃ：忘年会とは、その年の苦労を忘れるために行う宴会のことです。そして、忘年会を行うために職場の人と飲みに行くことが多いです。

The person who goes to drink with 職場の人 is unclear in C, so I rewrite it as D.

Ｄ：忘年会とは、その年の苦労を忘れるために行う宴会のことです。そして、忘年会を行うために職場の人が 他の 職場の他の人と飲みに行くことが多いです。

"職場の人が 他の 職場の他の人と" in D is lengthy, and "忘年会を行うために" could be written as "そのために", so I rewrite D as E.

Ｅ：忘年会とは、その年の苦労を忘れるために行う宴会のことです。そして、そのために職場の人が一緒に飲みに行くことが多いです。

I'll show my attempt for E as follows.

A year-end party is a party to do in order to forget the hardships of the year, and co-workers often go out drinking together for it.

Answer 2

Warning, this would just be my guesses.

のことで: First of, I would rather think that で is acting here as marker of reason for something. Like :

End of the year parties, because these parties are there for forgetting past year's hardships, many people go to them with they co-workers.

or something similar.

As for のこと, I don't really know. I do remember Japanese using のこと when they mean to emphases that something is the entirety of something. Like if you wanted to say you don't like someone at all, you might append のこと after their name to imply your not liking referrers to the entire individual. But I'm not sure if it's applicable here.

I'm also a bit unsure about the way I interpreted ことが多い, since I'm not 100% sure wether the こと references back to the parties or not.

Oh, I'm pretty sure こと here is just there to act as nominalizer for the previous statement that ends with a verb. So 職場の人と飲みに行くこと is:

going drinking with co-workers

and が多いです just means this is common.

Ultimately, 忘年会とは. I don't really know what to do with と

This とは is likely this one. Basically whoever is speaking is probably defining what the end of the year party is, what it means. What it is for.

At least that would be my 2c