The Federal Reserve says that non-financial companies are holding more than $2 trillion on their balance sheets, more than at any time in 50 years. Cash accounted for 7.1 percent of all company assets, everything from buildings to bonds, the highest level since 1963, the Fed said.

But “cash” is not necessarily… cash. That is, not necessarily piles of benjamins. The reporters that go on about Apple having $75-plus billion in cash are reading from a line in the company’s quarterly statement entitled Cash, Cash Equivalents and Marketable Securities. Cash Equivalents are things that can be easily converted into cash — stuff like bonds, or commercial paper, or even a money market account. Marketable securities are bonds that are also easily converted, but marginally less liquid than cash equivalents.

Cash to a company is a bit like fuel to the human body. The human body has several types of fuel available to it. It has carbohydrate deposits in the muscles, it has fat, and it has protein. Some of these fuel reserves are can be converted into energy very quickly, while others take a bit longer. The same goes for the cash equivalents that companies have in reserve.

I have a friend called Dan, who recently completed perhaps the most brutal triathlon in the world, the Norseman. It starts by jumping off the back of a car ferry into a freezing Norwegian fjord!

Anyway, Dan loaded up on carbohydrates the night before, so that he had a belly full of fuel when the race started. Those carbs were like instant energy to him as he swam two-and-a-third miles across the fjord. If Dan was a company, that immediate fuel would be real cash, kept in a bank account, which can, of course, be used instantaneously.

Dan can’t eat when he’s swimming, so his next source of fuel was the carbohydrate deposits in his muscles. This converts very quickly into energy. In a company’s case, that step is the conversion of the company’s most liquid cash equivalents; money market accounts and mutual funds, which can be turned into ready cash with a phone call.

On the bike phase Dan had to climb 1,200 meters over 112 miles. By this time he was burning fat, a process that takes a little longer than converting carbs. If Dan were a company, at this stage he’d be selling so-called short-term marketable securities, such as commercial paper and short term treasury bonds. Again, all it takes to cash out is a phone call, so it’s pretty quick, but to sell this stuff, you need a market, so it can take a bit longer.

Finally, Dan got off his bike and started running. The final marathon on the Norseman ends at the top of an 1,880-meter mountain, so if Dan had burned through his fat reserves by this point, his body would have started in on the last of its fuel, the protein in his muscles. In a company’s case, this last reserve would be its long-term securities, stuff like corporate bonds, non-U.S. government securities and municipal bonds. Again, this is all pretty liquid stuff, and relatively easily converted, but it takes a little longer to turn it into cash, depending on the market.

In short, the cash that all of these companies have stored up isn’t really cash at all, or at least most of it isn’t. In Apple’s case, of the $76 billion you’ve heard so much about, just $2.769 billion is ready cash. The rest?

We don’t get may people asking why companies are hoarding cash. Maybe people realize that businesses are in the same boat as the average consumer these days. The economy is in such a poor state, and the future is so uncertain, that companies are no more willing to spend money than the rest of us. Spending is risky when you have no idea whether you’ll even be in business in a month or two, and the bigger the expenditure, the greater the risk. It’s safer to hoard cash and wait for a rainy day. And in this economy, rainy days are never far away.