Investors poured a record $300 billion into money-market funds in just 3 weeks. Here's what they are, and why they're surging in popularity.

• Investors are pouring cash into money-market funds after SVB's collapse rattled confidence in banks.
• Assets in money-market funds reached a fresh high of $5.2 trillion on March 29. 
• Here's what money-market funds are, and why they've surged in popularity in recent weeks.

The biggest bank collapse since the 2008 financial crisis has triggered an exodus among the fearful: US depositors migrating their cash into money-market funds.