1) The word "triangle" contains four vowels: I, A, E, and E.

2) The concept of proportional representation, used in some electoral systems, aims to ensure that political parties' representation in government aligns more closely with the proportion of votes they receive from the electorate.

3) The concept of federalism involves the division of powers between a central government and regional or local governments, allowing for shared governance and autonomy for different levels of administration.

4) The first consumer digital video recorder (DVR), the TiVo, was introduced in 1999 and allowed users to record and store television programs for later viewing.