1) Grand opera is focused on spectacular production elements, sometimes at the expense of music or plot. It a gene of opera that appeared in 19 century. This genre is usually characterized by its special structure, large-scale casts and orchestras, spectacular design with lots of stage effects. The term "Grand opera" is actually came from French names of certain productions of the Paris Opéra of the previous century.
2) A leitmotif is a theme created by a series of slow moving chord progressions. This term is often defined as 'short musical phrase' because it is usually appears as a short melody, and either as a chord progression or a simple rhythm. It helps composers to bind a work together into a coherent whole, so that the story will be clearly understood and perceived without any words.
3) A series of songs that tells a story is known as a song cycle. A son cycle is a set of related songs which are connected one with another by a common storyline. They are meant to tell a story, divided in pieces where each one plays a big role in compiling the whole story. One of the earliest series of songs appeared in 13th-century, and if you are quite progressive in modern music, you can find out that many nowadays' musicians still record albums in that way.
4) Wagner believed that music was the most important element of opera. Actually, he thought that any composition or performance must follow the concept of Gesamtkunstwerk and the technique of leitmotiv, but it is obvious that all that is impossible without musical series. 'Music seeps through people's minds, makes their hearts beat quicker or slower, it shapes the perception of aesthetics, First goes music, then a setting and a chorus etc'.- Wagner was sure.
5) A symphonic poem includes only one movement. A symphonic poem is a piece of orchestral music that usually appears as a single continuous movement, so it is sort of independant part of the whole composition that plays one of the biggest role in the whole musical work.