Holding company depository receipts, a type of ETF marketed by Merrill Lynch. Unlike other ETFs, HOLDRs can only be bought and sold in 100-share increments. HOLDRs do not have creation units like other ETFs, but investors may exchange 100 shares of a HOLDR for its underlying stocks at any time. Existing HOLDRs focus on narrow industry groups. Each initially owns 20 stocks, but they are unmanaged, and so can become more concentrated due to mergers, or the disparate performance of their holdings.