speaking the lingo

One of the cool things about an industry (any industry) is the specialized lingo that is utilized by those in the know.
In IT we had certain words and phrases and in-jokes (all of which by now are probably so out-dated as to be useless): "Reboot it, you must", "Ping him and see if he's coming", "We tried to get lunch at that great Thai place but 404'd", etc.

I am happy to report that now in my 10th year in finance, the last several of which have been spent on the trading floor (I literally sit in the middle of the trading floor between trading, sales, and structuring), I have picked up a fair bit of the lingo into my regular English, to the confusion and consternation of my non-finance acquaintances.
Most of the lingo is because we're basically a lazy bunch and don't want to waste time saying long words and sentences. So for example if a bond is trading at 102.75, 102.50, 102.25, etc. everyone (or at least anyone who cares about the bond) knows that the handle is 102 so you can just say "50" for the price.
For quantity, bonds are generally quoted in yards. A yard is USD 10 million or JPY 1 billion (1o-oku in the mother tongue).

You are willing to buy at your bid and sell at your offer. Easy to remember because you offer something to sell like you offer tea and biscuits to a guest, and you bid to buy something like at an auction.
The market is the street.
If a trade is agreed, it is "DONE".
If you buy at the quoted offer, you lift the offer.
If you sell where there is a willing buyer (a bid), you hit the bid.
When there is much buying in the market, offers are getting lifted in the street. This makes sense because more buyers tends to push or lift the price up; as offers get lifted, offers go higher because with much demand to buy, sellers sell at higher prices until buyers stop buying, i.e. bids are pulled.

If you are told "half at fifty done" then you just bought half a yard at a price of [handle] + 50 (or .50, depends what you bought).
If you are told "fifty at half done" then you just sold same.
(I always get that mixed up, so there is a 50/50 chance that's backwards!)

A market-maker (someone who provides liquidity, i.e. is willing to buy and sell) quotes (tells) to the market his bid/offer; and generally you are willing to sell (offer) higher than you are willing to buy (bid) so a quote of "100/120" means willing to buy at 100 and sell at 120. So I guess technically it's an offer/bid but everyone says bid/offer.
If bid/offer is higher than previous, then it is widening. Lower than previous, it is tightening. Generally (though depends on your position) wide = worse market, tight = better market, similar to stocks where an up market (higher prices) is generally good and down (lower prices) is generally bad.
Then again, if you are short (sold more than you bought) in a down market, that's good; it means you can buy back cheaper what you've already sold for higher.
If you are long (you own it) and the market is up that's good; you can sell for more than you bought.
This gets confusing when talking about credit derivatives, particularly credit default swaps (CDS), which are basically insurance for bonds.
Easiest way to think about it is you are buying or selling credit protection. The protection buyer is buying CDS, paying some fixed amount (generally a couple of times a year for 5 years). If there is a credit event (for example the company goes bankrupt and can't pay the coupon on the bonds) then the CDS (protection) seller has to pay the buyer the full value of the bond.
If spreads are widening, that means insurance is getting more expensive, which means sellers are more convinced that the odds of a credit event are higher and therefore are only willing to sell protection at a higher price.
This is the same as a life insurance company charging more for a policy for someone who smokes, or car insurance being more expensive for teen-age boys; higher risk of death/accident so the protection (insurance) costs more.

And now a wee bit on accounting, while we're here. (The below is basically the sum total of my trading accounting knowledge. Shockingly little, eh.)

Where it gets tricky is in mark-to-market. The price out on the street is the market, and when you mark your book you set the value of the longs and shorts in your trading book to what the going price is in the market.
So for example if the CDS market is widening, that means people think there is a higher chance of credit events (problems) -- sentiment is that things are getting worse -- so protection (insurance against credit events) gets more expensive.
If you have been actively selling CDS (selling protection, which means taking risk) then you are short protection and long risk.
This means the protection you sold for 10 now costs 15 to cover; if you want to buy the protection you already sold, and be flat (no risk) you have to pay fifteen, for something you sold at 10. You lose 5.
Another way to think about it is: you sold something for 10 yesterday, but if you did NOT sell it yesterday and waited to sell it today, you could have sold it for 15. Then again, selling protection into a widening market is risky; you are taking on risk just when the sentiment is that things are getting worse.

Best usage I heard of mark-to-market was one of the traders talking about how his girlfriend (a former model) went to the Tokyo Motor Show (more famous for the scantily clad women who adorn the cars on display) so that she could mark-to-market, i.e. see how well she compares to the current crop of beauties.