Long term bonds have high interest rates and are quite volatile, which works well in some portfolios but not in others. They’re particularly popular in portfolios that seek to profit in a variety of different economic conditions. If you’re looking to add several uncorrelated assets for regular rebalancing purposes, consider trying some long term bonds in your portfolio.
Long term bond funds generally have an average maturity around 20-25 years. The returns on the site use a 10-30 year ladder that mirrors popular index fund methodology, but the results are also decent proxies for long term bond funds with longer maturities between 20-30 years. They are based on the highest quality bonds issued by the treasury of the country in question.
Different countries have different names for treasury bonds. In the context of this site, treasuries, gilts, and bunds are all interchangeable.