Expense ratio

The annual fee a fund charges, expressed as a percentage of the money you have in it.

Example

A 0.05% expense ratio costs about $5 a year per $10,000 invested; a 1.5% one costs about $150.

The fee is charged whether the fund goes up or down that year, and it compounds against you for every year you hold it.

Fee drag — The compounding cost of fees over time, which is far larger than the fee's annual percentage suggests on its own.
Active management — A fund manager, or you, picking specific investments in an attempt to beat a benchmark.
Passive management — Buying a broad, pre-set basket of investments, an index, rather than trying to pick winners.

A fund is a wrapper, not an asset class of its own — Buying a fund buys a proportional claim on whatever it holds. Until you have opened the holdings list, the name on the ticket tells you almost nothing about what you own. (9 min)
The fund manufactures nothing: pass-through, minus costs — A fund's return is the weighted return of its holdings less what it charges. Knowing that changes what you are actually forecasting when you forecast a fund. (11 min)
Appraising one fund: the holdings file, the rules, and the gap to the index — Seven checks, in order of how much they change what you own. The two everybody runs - the name and the expense ratio - are the two cheapest, and the one nobody runs is where the exposure lives. (14 min)
The cost you can read, the costs you cannot, and the tax bill you did not choose — Four layers of cost sit behind one printed number, and a fund's own trading can hand you a taxable event on a position showing no gain at all. (13 min)
Active versus passive investing — Trying to beat the market versus simply owning it. One costs more and rarely wins; the other is unglamorous and usually does better after fees. (11 min)
One scheduled review beats constant tinkering — A yearly review checks allocation, concentration, costs and whether holdings still match their purpose. Doing it on a schedule, in writing, prevents both neglect and reacting to every market move. (9 min)