I prefer not to get caught up in definitions, but rather to focus on what the intended purpose is. If you have an AA strategy that includes keeping a portion of your investments in fixed income, you can select from CDs, bonds, money markets, or other similar types of investments. The purpose of the fixed income portion of your portfolio is to provide some stability against the volatility of the stock markets.
It could be argued that in today's bond environment, only very short term bonds may actually provide this stability, or at least the perception of it, since we have no idea how long interest rates will stay this low.
For purposes of AA strategy, I see no problems with substituting a 5 year CD in place of an intermediate term bond fund. The yield is currently higher and there is no real volatility since the principal is guaranteed. Intermediate and long term bond funds actually introduce enough volatility that it could be argued they are counter to the purpose of having fixed income in your portfolio.