Liquidity preferences - Also described in the article as "investors escape safely on Preference stacks", investors usually have terms which state that when the company is sold, they get paid first so that they can at least recoup their investment before anyone else gets paid. Usually they get paid again with everyone else, resulting in a "double dip" into the sale proceeds.
Reverse-merger IPO - this is a rare (for tech companies) deal structure where private company A merges with public company B. The resulting merged company is now publicly listed because company B has already gone through the IPO process.
Dilution - described in the article as "over-dilution" and "dilutive financing", if there are X shares of a company and you own Y shares, then you own Y/X % of the company. If the company then creates Z shares to sell to investors, you own Y/(X + Z) % of the company. The difference between these percentages is dilution. Often, existing investors have anti-dilution provisions. They are able to buy additional shares in the round up to their existing percentage. Founders and employees usually have no such luck.
Ratchet in a down round - Admittedly, I don't know what a ratchet is. I would guess that it is a protection of some sort for investors from a down round and thus bad for founders and employees.
Non-liquid - (nearly) impossible to sell
Highly volatile - a plot of price over time looks like a rollercoaster
Anti-dilution provision - see the latter part of "dilution" above
IPO protections - Also have no idea what these could be. I would guess at something to protect investors who invest at a high valuation where the public valuation is lower.
409-A pricing - How the shares are assigned a value for tax purposes