But, I am bit confused with the first default selection option 'Search termbases sequentially until a matching term is found' under Multiple termbase search in Search Settings Window.
Can we view the searched terms of different termbases by selecting this option? Or this option enables the term search only in default termbase (one termbase).
It's actually explained rather clearly in the Help function:
In the Multiple termbase search area, choose one of the following options:
Search termbases sequentially until a matching term is found – searches each termbase separately and in turn, until at least one matching term is found or until the Hit List is full. If there are no search results for a given termbase, the search automatically continues in the next termbase, as defined by the termbase search order. The search stops as soon as the first set of results is found; within each set of results, matching terms are listed alphabetically under the termbase name. To resume the search and display the next set of results, select Next Search from the Search menu or press [Ctrl]+[N].
Search all termbases sequentially and group results by termbase – searches all termbases sequentially, according to the termbase search order. In the Hit List, the matching terms from each termbase are grouped together in alphabetical order under the termbase name.
Search all termbases in parallel and group results by term – searches all termbases simultaneously. In the Hit List, matching terms are listed alphabetically. In the case of a fuzzy search, matching terms are listed according to match value, with the highest match values being listed first.
Is it important to tick the Match Indexes check box?
No idea, TBH - I have it unchecked, and multiple-termbase search works like a charm.